Mitchie, the AIW (All-in-Wonder) line basically includes TV tuner functionality on the card. You can check an Anandtech review or ATI's website for more info, but it basically means you can watch and record TV on your PC.
My final recommendation is your choice.

The GT is a nice card at a nice price, and it has SM3 functionality which allows for nicer special effects on a handful of current games. The AIW XT is also a nice card at a very nice price, just that you're basically trading SM3 for TV tuner functionality. Both cards have 256MB and 16 pipelines and are plenty fast. The GF6 series seems a bit faster per MHz, but the XT's core does have an extra 150MHz on the GT's. Both cards may be limited by their 500MHz DDR memory, though. I don't know which to recommend for BF2, as I don't know if the XT's higher core clock or the GT's higher potential efficiency will yield better framerates (and possibly nicer special effects with SM3 on the GT). Either card should be plenty fast for CS:S and BF1942, so those aren't really factors, IMO. If you want to be precise, I know the XT will be faster in CS:S (look at any
benchmark), and I'm guessing it'll be faster in BF'42 (as ATI has a
slight edge in BF:V).
If the GF6's SM3 and HDR features matter not a whit to you, and if they won't be exploited in BF2 for SM3-exclusive special effects, I'd probably go with the AIW XT, as you do get at least ~10% higher performance for the ~10% higher price--plus the tuner, for recording shows on your PC. SM3 is my only hang-up, but it may not be an issue with BF2 (and it isn't with HL2 or BF'42)