Hi Mac,
First up, welcome to the world of PC Building. Be warned - it gets addictive
Your specs look pretty reasonable, and the components should be compatible but I've a couple of observations:
1. Currently, Intel tend to have the edge over AMD on processor performance. I'd look at a Core 2 Duo rather than the Athlon 64 - I presume you meant 5600 rather than 6500. For your price, you could just about get a Core 2 Duo 6600 which is an excellent processor.
2. The motherboard you selected has built in ethernet, so you wont need the NIC.
3. Your hard disk is almost certainly using the older Parallel ATA standard. This will get you going, but you'll want to upgrade to newer Serial ATA drives - possibly running in RAID - sometime in the future.
4. The graphics card you've selected is a good card, but it's one generation behind the latest and greatest. Of everything you've selected, this is the one component that may not last 4 to 5 years. To be honest though, even the latest and greatest will be badly out of date in 5 years so I wouldn't worry about it.
5. Cooling may be a problem - your graphics card and processor will be kicking out a fair bit of heat - especially during gaming. Without at least an exhaust fan on your case, its going to get pretty toasty in there and that can cause system instability and even failures. Check your case. It may well have holes for mounting 80, 92 or 120mm fans. If it does, get some. Your motherboard has headers for powering them.
6. Windows may very well not just start. Even if it does, if it came with your last PC, it will most likely be an OEM copy and only licensed to run on your original PC. If it does start, it may decide you need to activate again and might balk because of the new hardware. That said, I have heard of recent successful re-activations with only the hard-disks carried over from the old machine. Whatever else you do, back up anything important on the disk before you start your new build.
Best of luck with it all - its really pretty straight forward. Let us kinow how you get on.