I recently (Jan '07) used some old hardware and a PVR-150 (€90) to set up a MythTV box. I used Ubuntu 6.10 Edgy Eft because it makes everything soo easy.

Hewlett-Packard HP Compaq dx2200 Mini Tower
Intel Pentium 4 3Ghz
Board: MSI 0A48
512mb RAM
80GB Maxtor 6V080E0 HDD
ATI RADEON XPRESS 200 Series
Hauppauge PVR-150 with remote

I started here:
Ubuntu.org MythTV guide
Irish Channel Information is here:
NTL Ireland
Got listings to work using:
Mythtv.org UK_xmltv guide
Got the remote to work:
the mythttv.org guide to LIRC on Edgy
Other handy tips and tricks:
MythTV tips (Fedora focused)
Garry Parkers great MythTV Edgy DVB UK guide

Notes:
Took about 6 hours to get everything up and running
Issues with Mythfilldatabase? probably because your .xmltv file is in the wrong place
You'll probably have to set up your own channel info manually in mythtv-setup