yahoo/hotmail mail timing out.

Hello all,
here is a summary of my problem. I have a Win2000 server that serves as a proxy for about 50 Win98 machines. Connection is thru DirecPC for downloads, dial up for connection. ICS is set and there aren't any blocks on any sites. The problem is that both the proxy and the clients can't get any mail downloaded and neither can they compose. This happens on both IE and Netscape. The connection times out even when set to go for 3 minutes. I set up a maxMTU in the registry for the direcPC satellite card to 1375 but no good.
Do you folks have any idea of settings to check/change? any ideas would be appreciated.
Brent