Issue with SBS 2003 and Cisco Pix506

OK, Here’s the setup.

Cable Modem to Cisco PIX.
Cisco PIX(192.168.2.1) to 2nd NIC in SBS2003 Box(192.168.2.5)
1st NIC in SBS2003 box(192.168.1.5) plugs into switch to the rest of the network.

My server does the DNS and DHCP.

Here’s my weird issue. Once in a great while, the server will decide to do NAT (i assume), and i have to fight it NOT to. I’ll lose my internet connection, i’ll have to reboot my Cable Modem, PIX and Server. Once everything comes back up, the Internet connection is REALLY slow… (i’m lucky to get 1Mbps when we should have 6Mbps)

If I plug a laptop into the PIX and test the Internet, it zooms! But once i try it on the server or from behind the server, it drags!

Any Ideas?