A local computer shop has the following HP refurb without an OS for under $500 CAD. Is it worth the potential mess of dealing with HP hardware or should I just piece together a machine and pay a little more?

Processor: Intel™ Pentium™ 4 Processor
3 GHz | 1 MB L2 Cache
Chipset: Intel™ i945P/PL/G/GZ
Memory: 1024MB DDR2 (2 × 512 MB)
Expandable to 2 GB
Video: Integrated video
Audio: Integrated High Definition 7.1 audio
TV-Tuner: TV-Tuner/Capture Card with Microsoft Remote Control
Hard Drive: 200 GB HDD
Optical Drive: DVD+/-RW Multi-Format w/ Lightscribe
Media Card: 9-in-1 Memory Card Reader
Network: Realtek 10/100 NIC
Fax/Modem: 56K V.90 Modem
Interfaces: 6 - USB 2.0 Ports
1 - RJ45
1 - RJ11
Microphone In
Headphone / Audio Out
Remote Control
Inputs: S-video, Composite

You need more information about the tv tuner and remote control to be sure they will work with knoppmyth. Personally I would make my own system. But for $500 CAN that sounds like a pretty good deal.

The main issues I see are the ones ryanpatterson identified and the onboard video, which you're probably going to want to override. Also, unless you're going to do HDTV the 1Gb of RAM is overkill, and the modem is likely a "win-modem" which makes it a useless waste of a slot.

The other issue I'd check is noise/heat. Have you actually seen/heard this box running? Remember to take into account that what might seem relatively quiet in a shop with a lot of background noise may sound like a vacuum cleaner in your livingroom.