I think the drivers are fine. Where more attention is needed with 64 vs. 32-bit is the codecs. For example, Vista x64 has both 32 and 64-bit versions of media player (32-bit is default) but media center is 64-bit. Since codecs are 32-bit or 64-bit specific you may find some media files will play in media player but won't play in media center, for example. Same goes for Internet Explorer... 32-bit and 64-bit are included (32-bit is default) but no flash yet for 64-bit.
Also, if you are interested in mkv files, AFAIK haali has not come out with a 64-bit splitter. A work around is to manually register a separate 64-bit matroska splitter.
In short, there's just a little extra work needed for 64-bit right now.
Concur with Scotteq.
I'd first verify all drivers would work w/64. Then only question is from a performace issue. Which is faster, less overhead. You probably do not need in excess of 3 gigs (go for 4 - 2 x 2 sticks). Woul not let the loss of approx 1/2 gig of ram in 32 bit aeffect my choice. If down stream you plan on going with more ram, then you have to go with 64 Bit - BUT concur w/alvine, Driver/programs support still favour 32 bit due to Nrs inuse ( that will change as more 64 bit OPs are sold).
heres what's actually important to me (in order):
1. playing .mkv videos
2. streaming videos
3. light web browsing
4. playing blu ray dvds
i dont care too much about recording things as I can pretty much download anything I want. Plus, the only regular programming I watch are news+sports.
ps. do i even need a tv tuner for my htpc?
Since you didn't list OTA/Cable/Sat as one of the things you want to do with your HTPC then I would say no you don't need a tuner card. If all you are using it for is web and file based viewing then the tuner would serve no purpose for you.
You mentioned Bluray discs as well. The software you are using to play those will have a lot to do with the bit version of the OS you install.
Get a list of the programs you use to do all of the things you listed above.
Verify that all of them have working 64bit versions. If they do, you are probably in good shape for a 64bit OS. Otherwise go 32bit.
For the applications you are using the PC for, it wont make that much of a difference either way. Application support (as well as drivers) is going to be your biggest concern. Using 2GB of RAM will handle what you have listed easily.
Take it from me, I am reinstalling my Win7 right now to go to 32-bit. 64 bit was nice, and support is getting there, but you will hit roadblocks with 64-bit hardware support. My stupid Hauppage card is causing me to go back to 32 bit. Perhaps one day, when 64-bit is the norm, I will up the HTPC to that again. The problem is all the tool(z) you may encounter out there are written for 32 bit first. Until people are forced to go 64-bit, this will remain the same. Trust me, I've wasted too many hours of my life just becuase I wanted to go 64-bit. Maybe next year? who knows.
There is no x64 bluray support to my knowledge. Also the best decoders (i.e. codecs) are all 32-bit. E.g. coreAVC for your x264 MKV's gives the best PQ and the lowest CPU use but is 32-bit only. Ffdshow, the best codec for anything else (xvid, etc, is both 32 and 64 bit but works much better under 32 bit. Audio codecs for aac, m4a, flac etc also work well under 32 bit and hardly under x64.
In addition getting 3rd party filters like CoreAVC, ffdshow etc to work on windows media center is almost impossible under win7 and every new version disables more of them. Extensive hacking is required to get it to work.
On the other hand Vista 32-bit works flawlessly as an HTPC platform (which means no other software installed, just the OS, a few codecs and some other video applications e.g. a bluray player like Arcsoft media theater). I also tend to disable auto updates so I can control the configuration and keep it stable.
So, for a trouble free Media Center PC, I definitely recommend a 32 bit build, even though I am a huge fan of Windows 7 and prefer 64-bit OS's generally. They're just not suited to this. I use Win 7 x64 on my workstation and Vista 32 on the HTPC - I'll upgrade it Win 7 in something like 18 months when all the bugs have been worked out and the hacks automated.