OK, after running mixed networks etc, i know some of your problems. Win98 and network cards sometimes have problems seeing eachother in the network. The best thing to do is leave the computer up that can see itself in the network, or rather leave the one that can see the rest of the network - if this applies, then reboot the other. Goto network neighborhood, refresh several times.. over the course of say 5 min. Another thing, if you have a lan connection and you are using internet as well, sometimes it helps to make sure your tcp/ip settings are similar.
Windows 95 has more problems with seeing other computers on a network than 98. I've seen sometimes when i boot up my win2k box, and then my windows me box, they dont see eachother, i leave the win2k box up and reboot the other and this solves the problem.
I also have a 98se box that originally had windows 95 on it, None of the computers in my network can see it, but it can see every other one. I belive this to be some confilicts with installing 98 on top of 98. The best way to have a network work properly is to have a single OS network, not a mixed network and make sure that each OS matches- win98 se, and win98 have been known to have problems.
Hope this gives a little insight.