very low budget HTPC build, advice needed

[tech-wreck]

(as i'm new, quick intro)
hi, i'm andy, and i like to hack stuff. sometimes, it works

anyway, i want to put together a HTPC, for basically £nothing. my tv and projector are both 720p, so i don't want to spend full HD money until after i get a new one.

i read somewhere (possibly on TH) that a socket 775 mobo is capable, if that's right then i'm halfway there. maybe.
i have an old dell optiplex gx620, with a pentium D 3Ghz in a 775 BTX mobo. i know it needs a GPU, some more RAM is already in the post.
i would guess the processor needs an upgrade, and the power supply too, it's only 250w or something.
the case is junk, as i will be putting it in a custom box, so no worries about large parts not being able to fit.

so, will the components i already have be suitable as a starting point? and what GPU will i require (i have a spare 9800gtx - would that do? ( i'll definitely need a new PSU to power that thing! ))
thanks in advance, all advice/suggestions will be gratefully received, even if it's "stop being tight and go buy something off the shelf"
cheers
andy

ps, why does it keep popping up telling me to write properly? i can english!

 

[tiny voices]

The optiplex gx620 has a proprietary motherboard which will not fit in a standard case because it is not ATX, mATX, ITX.

 

[giantbucket]

Nearly any modern CPU (that has built-in graphics) can play 720p movies without needing a separate GPU.

If you really want a GPU, then something like a silent / fanless GT610 would be A-OK. Less than fifty quid.

 

[tech-wreck]

The optiplex gx620 has a proprietary motherboard which will not fit in a standard case because it is not ATX, mATX, ITX.

i'm sure i mentioned it was BTX. and it's not going in a standard case, i am custom building something. it will be made to fit. with flaming hammers if necessary.

Nearly any modern CPU (that has built-in graphics) can play 720p movies without needing a separate GPU.

If you really want a GPU, then something like a silent / fanless GT610 would be A-OK. Less than fifty quid.

i'm trying to re-use and re-purpose whenever possible, if i can use my existing hardware and only upgrade what is necessary, great. if i go down the modern CPU route, i'll also need a modern mobo to put it in, etc.
i think i need to get the tools out and do some hardware juggling. i will keep that fanless GT610 in mind, i'm sure i've seen them cheaper than that. i'll update when i've had a tinker
cheers
andy

 

[tech-wreck]

update:
1: the onboard graphics will play 720p content (streamed from youtube), good quality video but with noticeable and increasing audio lag. not sure if hardware or software causing that.
2: a 9800gtx will not fit unless i take a hacksaw to the serial connector/socket or the GPU bracket. i'm not that desperate. yet.
...
*goes shopping*