hmm
similar problem here

my comp A is Athlon 1.2GHz using SMC 10/100
running win2k sp3

comp B is P2-300MHz using D-Link 530-TX+ (same as urs)
running win98 se

Router
Macromate MSHR-8104
10/100 ADSL/cable 4 port router

cables are fine...
100 mbits light is on the router
no problem there

no ports restrictions or hiding

but when i want go to the drive directory page of comp B from comp A, it lags and the windows "busy" hourglass come up for that network explorer window
it "stalls" for approx 1 min then shows drive C and D
which are the drives on there

why is it so slow?
i dunno
but since Omega suggested EMI, im considering it too
because ive got too many wired running behind the comps along with the cat-5 cables