Wow – not a lot of information here, I’m assuming you mean the computers are slow to talk on the network, but they are fine locally. Some of the things you are going to want to check for slow network access:
1. The switches the computers are connected to – what speed are they.
2. The cabling – is cat 5 or better?
3. The cards in the pc’s what are they set to/capable of.
There are a myriad of other things that could be causing issues including routing and dns – we need more information to be able to assist you better.