Now that that's out of the way let's build a video capture system from the motherboard up. For video capture you want to avoid motherboards with on-board graphics controllers (the Intel 810 series chipsets are particularly notorious and should be avoided). NIC controllers on the motherboard can also cause problems unless they can be disabled during video capture. ATA-66 or ATA-100 on the motherboard is preferable to using separate controllers, but SCSI on the motherboard can cause problems in some systems if it is 'hardwired' as controller zero. The most common problem with installing video capture devices arises from IRQ conflicts. You should also check with the motherboard manufacturer's Web site to make sure you have the latest and greatest BIOS. I've heard that there were some early problems with some HP systems and some capture boards until HP upgraded their BIOS.
If you're like me then one of the basic criteria you use when choosing a motherboard is that it have lots of slots. You should be aware that some capture cards like to stick 'close to home' (usually first or second slot after the AGP slot) and don't function well on the other side of the PCI bridge. Some, like the Pinnacle DV500 Pro, are very picky about this so be prepared for some swapping if things don't go right the first time you install a new capture card.
As far as CPUs go the minimum speed is about 300 MHz. As I mentioned in part 1 of this article CPUs don't play a major role during capture but they are called upon quite heavily when you start doing transition effects, rendering, or transcoding from one CODEC to another. Most manufacturers support both Intel and AMD CPUs but get a little touchy about others. If you're building a new system from scratch then you should probably be thinking about an 800 MHz or better CPU. Overclocking is not recommended since many capture cards derive their timing from the CPU and, unlike most software applications, video is not flexible about this.
Memory is a good thing when doing video capture and most companies recommend at least 128 MB - 256 MB. Speed and type of RAM aren't that critical so if someone tries to convince you that you need a dual Pentium Xeon with scads of RDRAM you should probably look for another dealer.