Yeah that AVS thread is really like an encyclopedia when it comes to HTPC set-up. So I'll try to give some practical guidelines to complement all the information you can get from that site. These are just my opinions.
CPU: AMD or Intel. Doesn't matter. Just buy the fastest, meanest multi-core Intel or EQUIVALENT AMD that you can afford. Intel's E6xxx and Q6600 seem to be very popular examples. Any of these multi-core CPU's will make you happy but the more powerful the CPU is, the happier you will be for that blood thirsty MKV contents, especially 1080p ones. Just like to stress once again, CPU is the most critical component at the moment for MKV playback. You need to do some reading on the current line of CPUs and find your sweet spot in terms of budget. No need to delve on full technical details. For starters just look at the clock speed, the number of cores and the front side bus speed - and then make 100% sure that your chosen MOBO supports the CPU. New models of MOBOs are OK in terms of compatibility but if you are buying an old model MOBO, then be very careful
MEM: It appears the mainstream type right now would be the 667 or 800Mhz DDR2 (dual channel types). You don't need to buy those expensive and cool looking Corsairs with 1066MHz clock, but I would recommend reliable makes such as Crucial, Kingston, Buffalo, I/O Data, etc. Nowadays there are 2 types of "bulk" memories; the "totally generic" bulk and those with rather "unpopular makes. You can save money by trying them as well. Compatibility with popular MOBOs is not 100% guaranteed but working chances are very high. If your PC is retail (Dell, etc.), then stay away from generic mem. For Vista, you need at least 2GB. For XP, you need at least 1GB. However, I personally think the sweet spot for MKV is at least 2GB. BTW, dual channel memory banks should be installed in PAIRS, otherwise, it would run at half the rated clock speed. So if you want 1GB of mem, then you have to install 2x512MB using the appropriately paired (usually color coded) mem bank slots in your MOBO.
HDD: A 720p MKV is at least 4.5GB big. 1080p can range from 6B to 40GB. Get as much GB as you can afford. Seagate, Western Digital, Samsung, Hitachi...doesn't matter which make. 7200 rpm, 16GB cache has become the mainstream. You don't need those expensive models with higher cache for your personal application
Sound Card: If you are not that picky, the on-board 7.1 channel audio of most modern MOBOs is more than sufficient. Confirm that optical out (SPDIF) is available on the MOBO (it usually is for new MOBOs) if you want to go multi-channel connected to an AVR. Otherwise, you need a GOOD 2.1 channel set of PC speakers at the very least. Something with powerful subwoofer like that of Logicool Z4 would be nice. But if you already have a multi-channel AVR and speakers set HT, then just connect your PC to the extra optical input of the AVR.
Video Card: You mentioned "little gaming" but how little is little? Once the word gaming comes out, then you can forget about the on-board video unless your image of gaming is Free Cell. The general consensus is that Nvidia is better for gaming overall but AMD/ATI is better for HTPC, BUT, if you are interested enough to analyze the detailed performance of each particular model, you'd find out that it really depends on the particular GPU. Doesn't matter which maker you choose because most of them follow the reference design provided by Nvidia or ATI, then just put their logo on the fan.
As I personally confirmed recently, you definitely don't need a high end card like HD3870 or 8800GT for an HTPC. Depending on your gaming needs, I think you'd find your balance on any of the following GPUs: HD2600XT, HD3650, HD3850, 8600GT, 8600GTS. Cheaper cards MAY work just fine but the determining factor here is the kind of games you want to play, not the MKVs you want to watch. More expensive cards are definitely overkill.
You may also want to read on the reviews of the new MOBOs based on ATI's 780 chipset with integrated graphics.
Casing: Totally subjective. Some like it vertical, some like it horizontal with "AV equipment look". Some like it in whatever kind of color, some prefer vanilla beige or pitch black. Some like it with transparent window with a nice view of the innards of the PC, some prefer the traditional "closed" container. Some like it cute and slim, some like it huge and imposing with lots of spaces for future expansion and additional cooling.
Power Supply Unit: If your interest in gaming is not that much, PSU wattage and amperage are not critical. However, the given ratings of the PSU should be HONEST and not simply overhyped specs, that's why popular and reliable makes are recommended.
I only started to browse through tipidpc this year. Yeah you can find some nice parts there at good prices. You don't need to buy brand new items, but make sure they are in perfect working condition. Stay away from "REPAIRED" parts.
The member Tambutsoo started a thread under Sources for an entry level HTPC less than 20K (including part models). Please have a look at that one.
BTW, how come nobody seems to factor in the cost of the OS license in the budget??? Is it "free" in the Philippines??? An OEM OS would cost me at least $100 in Tokyo
Finally, if you suddenly get afflicted with SARS of the HTPC strain, then PM me your hard to find exotic PC part and I can source it out in Tokyo.
