Network newbie needs help! Wierd lan/modem/browser behavior

Specs:

2 x ECS K7S5A's connected via lan crossover cable using onboard lan. Both machines also have the onboard ECS AMR 56k modems. I'm running win'98SE, netbeui, and have file and printer sharing enabled.

I'm using the SiS-900 fast ethernet drivers for the onboard lan, and the ECS AMR riser modem drivers too for win9x.

Both machines work beautifully when the lan is disabled in the bios. However, browsing sucks big-time whenever I enable lan in the bioses.

Symptoms:

Slow boot about 20 seconds to desktop without lan, 45 with lan. Should I expect this because it takes time to initialize the lan?

The worst symptom is during web-browsing. Even If I don't have the second machine turned on, I will frequently get a huge delay in IE 5 while on-line. This isn't true when I have the onboard lan disabled in the bios. But this modem "sleeping" is driving me nuts.

Yes, it stays connected, but when it falls asleep, neither clicking on links, refreshing, or trying to go "home" works. However, after about 60 seconds of not responding something happens and all is back to normal for a few minutes.

When the browser falls asleep, my machine is working, and I'm not getting error messages. It's like this freezing up/sleeping is some sort of time-out setting or something. When non-responsive, my mouse works, and I can jump in and out of the desktop. However, no on-line links will respond for about a minute. Argh!

I've also noticed sometimes that my dial-up connection will drag it's ass and wait for about a minute to start up. It's definitely something to do with the lan settings.

Is this sleeping while online a common problem for lan's? Are there tweaks in win'98 that I should use?

Thanks for your help,

-Brian