Normal throughput between connected computers?

Hello:
Just bought a Belkin wireless Pre-N router and a wireless Pre-N PCI adapter.
Now I've just tried setting up a network between two computers.
The first computer is wired to the router(100 mbit NIC) while the other computer in another room is connected via the wireless adapter. Everything seems to work fine. The signal strength to the wireless adapter is very strong and it's reported as running 108 mbps. Internet is fine as well and download speed very stable.
The only thing that is confusing me is that transferring files between the 2 computers are very slow or slower than I expected.
Transferring a 4.5 GB file takes about 30 min. Is that a normal throughput?
When transferring Windows Networking utility is only reporting a utilization of 10-15%.
Btw decryption is disabled. So is something wrong or is this normal speed in wireless network(if so kinda disappointing)

Thanks.