Linksys + Linksys = Conflict???

Hey, I thought maybe one of you guys or gals have encountered a similar issue.
It's purely hardware:

I have a Linksys Wireless Access Point Router with 4-port switch Model #BEFW11S4

I also have a Linksys EtherFast 10/100 8 Port Workgroup Switch Model #EZXS88W

The router is plugged in to cable modem - but that has nothing to do with the problem - I use 3 PCs that are directly hooked up to the router's built in switch and experience no problems..

The problem is: Since my 8-Port switch is plugged into the uplink port of that router, any communications between any PC plugged into the 8port and the pcs that are plugged into the router's switch are painfully slow - i think in the range of maybe 256kbps (And they are both 100MBPS switches!!). Communications between PCs that are both on the 8port switch are fine - fast as they should be, it is when I try to access the internet from the PC that is plugged into the 8port switch I experience major slowdown, same thing with file sharing accross switches...

The peculiar thing is - if I unplug the 8port and reset it, for about a minute or 2 it works fast and then it looks like it dies down... I tried replacing the 8port in warranty - same thing happens with new one.. My FD/Col light is always on on the 8port - i don't know if it means anything..

I also tried uplink on 8port and regular port on router and vice versa.. same thing...

Any ideas would be appreciated...

Thanks.