I had an issue where my 3945ABG wouldn't connect at all. After lots of fighting with it, Intel finally released a driver that works and it is on their site now called V11.1.0.5_XP32.exe

Try the latest Intel driver called V11.1.0.5_XP32.exe

I would definitly use 6513's for the core and 4500's for the IDF's. As for the DMZ, depending on the size, I would use a small 6500 or 4500.

Use a PIX 501 for a VPN end point. the standard license is 10 users but you can expand that to 50 or unlimited depending on the size of your remote sites.

In addition to that statement you need an access list that will allow the traffic in.access-list acl_out permit tcp any any eq 5000access-group acl_out in interface outside