Network slowdown

I have a small network of three computers.
The spec. is below. The two main ones are listed as the other is not relevant I have only recently purchased the PIII and ever since, the network has been very slow on high usage apps and games. I have tried a lot of things, such as reinstalling various things, etc. but it has not worked

Specification
A) PIII 450 128MB
B)Celeron 300A 128Mb

Both have Linksys 10/100 PciEther II cards
and a 5port hub