If you want to go low-profile, here's my experience after doing the exact same thing.
- AMD CPUs run hot. You will probably need to mod the case to allow for better air flow. I found that a Alpha PAL8045 with 80mm fan with a 80mm hole cut in the case directly above it worked great.
- TV tuner (if you want one) is a problem. There are a couple on the market, but are not very fancy.
- Your AIW won't work. PowerColor makes a 9200se and 9600se that are low-profile. They used to make a 9100, which I have, but nobody sells it anymore. If you want to do games, go with the 9600se, it's not all that bad. Newegg has them for under $100.
- For a case I suggest the AOpen H340D. Very good case that lots of people use. Newegg has them for under $50 after shipping. The cheaper ones from other manufacturers are much poorer quality. If you get the H340D, make sure the ATX power plug on your motherboard is on the side of your CPU closest to the PSU, otherwise you will need to get an ATX cable extender (about $10).
- For motherboard, if you don't need high-end graphics you could get a nForce2 board and have somewhat decent 3D support (GeForce4 MX440). I suggest either the Shuttle MN31n, or ASUS A7N8X-VM. Both should be under $100 if you shop around.
- As mcveigh suggested, a XPC would make life much easier on you. The only problem is that they are taller than a low-profile case. So make sure it will fit your space before you buy it.
good luck, and feel free to PM me if you want some pics of my systems. I have 3 low-profile cases, all modded for extra intake fans and such.