Linksys Router RT41-BU - hangups !!$%?

I have the AT&T speedstor 4100 and the wired linksys Model RT41-BU, and I have two PC's connected to the router (one is windows 98se, the other is windows 2000 sp4, a third, not yet connected is xp sp2).

When I bypass the router on either win98 or win2k, everything works great - fast access and pages are fully rendered. When I go through the router, access via win2k gets sluggish, some pages don't come up at all (gives the "TRY AGAIN" box), and some images are titled but not rendered. The win98se PC has the same problems, but, less so. When I cant get through to a given website under win2k, if i access that website with the win98 PC at the same time, then the win2k PC finally gets through also. This is very frustrating. Two aspects of having this router make me want to keep using it - I can share h/d's between the PC's, and, both PC's can access the internet at the same time. I usually have my win98se PC accessing liva radio, and reading email, and I use the win2k machine to search for subjects and reading online articles.

When I get the message "try again", it susggests that a firewall might be preventing access. The user's guide for the linksys router indicates that there is a Stateful Packet Inspection (SPI) embedded with cannot be disabled.

I need help in one of two ways:

a) Is there a better device (instead of the wired linksys router Model RT41-BU) that I could use between the PC's and the AT&T Modem (siemens speedstor 4100), that would allow me to share h/d's and also have concurrent access to the internet, but, WITHOUT the hangups that might be caused by the non-disableable SPI? or

b) Is there something I can do in software (in both win98se and win2k) that will bypass whatever is causing these hangups in the router?

I have been able to determine absolutely that these hangups are caused by the router - I simply power down, bypass the router and connect directly to the modem, boot up and all the access problems go away like magic - but I lose my shared h/d's and I can only access the internet with ONE pc at a time.

I lack experience and knowledge as to networking - maybe using a router is a bad idea, after all.

I do not need a firewall - both of my PC's are fully backed up and can be retored in a matter of minutes, should I pick up a virus. That happens occassionly, but, it is not a problem for me since I can format the C drive and restore from my backup so easily and quickly. So, if this router's SPI (firewall?) is causing these access hicups, then I would like to get a different device that wouldn't have a non-disableable firewall or any method that would disrupt the normal access I enjoy via the modem.

Help.