I primarily use Macintoshes, but at work I use an external display and keyboard; the keyboard I happen to be using is a pretty nice one from a Dell PC. One problem with using PC keyboards on Macs is that the Alt key and Windows key (which maps to the Apple Command key) are swapped between the two keyboard layouts. This makes command sequences frustrating to touch type in both MacOS and Windows.
I had found a little kernel extension, "DoubleCommand," that had a lot of remappings you could reconfigure, like "Enter acts as Cmd," "Backslash acts as forward delete," "Shift backspace acts as delete," and of course "swap Option and Cmd keys" which is what I used.
Too bad it became unstable and started causing kernel panics at boot time at some point around 10.4.9, forcing me to try to get used to the "backwards" modifier keys while at work. Supposedly the new version works perfectly with 10.5.2, which just came out, but...
Imagine my embarrassment to discover that 10.5 has, quite built into the keyboard control panel, a modifier key remapper. As a bonus, it lets you configure it separately for every keyboard type, eliminating the need to reconfigure DoubleCommand when I'm using, or not using, the PC keyboard.
Joe Bob says check it out.