I have a old dual P2 system laying around and I was curious to if I could make a decent HTPC out of it.. heres its specs.
N440BX intel board
2X P2s @ 400 MHz Per
256 MBs of ram
10 GB HD ( Plan to get larger if the other specs will do.)
Onboard Cirus Logic video ( plan to get some decent PCI card for it IF its worth it.)

wow.. this forums response time has went down the crapper.

If you want a true htpc that will run media centre edition and not just a media centre version of linux then sadly this specification will not do. For a HTPC i would recommend a minimum of the following specification:

Intel Pentium III 1.2Ghz Or Above
512mb sdram/ddr ram pc133 or better
80gb or larger hard drive to store movies and tv recordings
dvd +/- rw drive so you don't fill you hdd with too many recordings etc.
minimum of geforce 6200 or something cheap with the advantage of having hdtv and composite outputs
and of course a tv card compatible with mce for recording tv from cable, freeview etc
and if you really want to a mce remote or something to remotely control it.
That spec would do nicely for a media pc and would be quite cheap not £1000's or even $1000 of dollars just my two cents.

If it don't work try hitting it, then if that doesn't work buy a new one :P