If it is the switch then surely the only one you should need to change is the one connected to the problem box isn't it?
I picked up an Allied Telysyn 16 port managed switch on Ebay for £62 which is not bad especially for a Managed switch.
I see what you mean, but I haven't moved any switches to Gigabit yet. I'm just trying out Gigabit as I wasn't sure about my NL box. So I went and bought a switch at Staples and hooked it up to my NL box via a cat5e patch cable and since the NL box is in the same room as my PC I ran a cat 5e patch cable from it to the machine as well. The windows PC ran GB but the NL box didn't. I then swapped the cables and the same thing happened. I then tried every port for the windows PC and all showed GB and every port for the NL box showed 100mb for the Netgear NIC (I finally got it to 1Gb but it would shut off and bump down time after time) and 10Mb for the intel NIC. So I'm only playing with the one right now but when/if I get it working I have that switch plus I need 11 ports in my Home panel (so I'll prolly run 2 switches there since I don't have room for the bigger 16 port switch) and 5 port switches at my desk (Printer, PC, Laptop) and my wife's PC (Printer and PC) and the HTPC (PC and Tivo) so I guess I could run a good 5 port in by my NL box in that closet and the cheaper ones elsewhere.
I'm really starting to think it's just a conflict with the BIOStar MB and need to start looking at different hardware for the NL box. I have another post in the Hardware Section and may just go that route. The BIOStar MBs weren't expensive by any stretch of the imagination and prolly just have issues with the NICs. I'd really like to find some hardware that doesn't have issues like this. I never knew NL would have this type of issue with older hardware.