Well, basically you need to buy an IR PC remote... mainly to get the IR receiver. After you've found one, just learn the original remote into your URC100 and then put it away in a drawer.

Most PC remotes aren't too expensive... there's the StreamZap PC Remote (which I'm using myself with a laptop and an MX-800), Soundgraph iMon (very popular in the HTPC world and supports more commands), and then there's the good old Microsoft MCE remote if you're running Windows MCE edition (which I use for my main desktop PC). And of course there's more as well.

All of the IR receivers I've used have been pretty good, but the real concern comes down to drivers. The Streamzap is very basic but ends up doing everything I want; the MCE remote doesn't allow any customization really but controls an MCE system perfectly; and iMon is by far the most sophisticated but also probably the hardest to successfully replicate via a universal remote.