Network Speed - Slow on some systems

[EvilAlchemist]

I seem to being have a little speed issue with my network.

Network Setup:

Cable Modem - Cat 6 - LINKSYS WRT300N Router
Router - 3 x CAT 6 to Systems - Cat 5e Crossover to LINKSYS EG005W Gigabit Switch
Router - 3 x Wireless to Systems
Switch - 2 x Cat 6 to 2 Systems

It seems when I use "Radmin" or just browse files on the three systems connected to the rounter ... it seems to run slowly.

The wireless system and the two connected to the switch are very responsive. (Main Rig on Switch)

I have verified that the systems connected directly to the router are connected at 100Mpbs and systems on the switch are at 1000Mpbs, but i am no network expert ..

Is these some setting I am missing or have mis-configured somewhere?
Would it help to get a gigabit router? (All systems are gigabit ready)
Did I change or need to change a duplex setting ... at a lost .. cause i know nothing in this area

All systems running Windows XP Pro.