The issue when choosing hardware is how patient you are when waiting for programs to load. The minimum requirements for GB-PVR using a PVR 150 are a 1.2 GHz processor and 128 MB of RAM. With a FireFly remote I would suggest at least 512 MB of RAM and 1 GB if you're looking to multitask.

If you plan on doing video encoding such as burning your recorded shows to DVD when your hard drive fills up, I would suggest a faster CPU. What's fast enough for you? I suggest you look at some benchmarks. As an example, I have an Athlon X2 4400+ with a gig of RAM connected to three screens. An Nvidia 6600GT runs a 26" LCD TV connected via S-video and a 15" LCD, while an antediluvian ATI Radeon 7000 drives a 15" CRT.

My HTPC

Inside my tower. Note the two graphics cards

This configuration lets me multitask to a ridiculous degree and encode just about any type of video in less than two hours. I can also have Comskip run and not even notice. On the other hand, if your computer is dedicated to GB-PVR while Comskip is running and you never close GB-PVR then the minimum suggested requirements (1.2 GHz CPU,128 MB RAM) will do fine.

Another example is the recent transfer I did of my PVR system to an old Compaq running an Athlon 2000 with 512 MB of RAM connected only to my roommate's 27" LCD. Moving the system was easy; you just need to install the remote and tuner, then install GB-PVR and copy over your configuration files. This system uses the Compaq's integrated audio connected to a sound system via an RCA jack converter, so has lacklustre audio quality. So I could see the need for adding a sound card in the future.

My roommate's system

Inside the old Compaq