Low Network Speeds

I'm having a bit of a problem understanding what is going on with my network transfers and their speeds, basically i have two different setups which i connect to either through wireless or through a high speed physical LAN network (cat 6 cables, gigabit switch, Gigabit port on computers) Though the wireless everything is as to be expected slow as ever but it almost always works, with the cables often the network will connect but have no internet access (but i can access other computers ,which do have internet access). Also vista reports the network speed to be at 1Gbps (1 Gigabit) but through testing i have found it to be around 55 MBps (55 Megabytes, should be around 128Megabytes, i believe),

I have also tested the speed by connecting two vista computers together both with the required ports, vista says the link speed is 1Gbps but yet again i don't get even half this, anyone know what i am missing here??
and why i frequently lose internet even when the wireless works??

any help would be great



Specs:
Intel i7 920, Asus P6t motherboard, Gigabyte 9500gt 1gb, Seagate es2 barrcuda, 2gb ddr3 ram , trition 81 cpu fan + 4 case fans, Windows vista Basic, Windows 7 RC (dual boot)