Issues with two new Dell PC's mapping drives.

We have a room of 20 PC's which are P4 3.0 with all On Board devices (MSI) , At the start of term we needed to add 2 PC's into the ROM because of class sizes. We put two new Dell PC's in. These 2 Dell have 1gb NIC's and all the other PC's have 100mb NIC's

We find that when pupils log on to the Dells they randomly (more often than not) do not get their H:drive mapped but all the other 20 older 100mb Nic's map first time. I have updated the NIC driver on the Dells to the latest, configured the NIC to 100mb Full and also !100mb Half ad it has shown no change. This room is the furthest away on the five run but all other computers work fine.

I have today been told this is also happening on 20 of these Delis randomly as well. The 20 Dells n the other room are the same spec as the 2 Dells i mentioned earlier.

Does anyone have any idea what could be causing this?

Is there any chance they are geting to log on with cached credentials and the computer hasnt actually connected to the network properly yet so no mapped drives? I get this sometimes.