im with Paul on this one.

Since you say a 700MB C: partition i assume you have windows XP or lower.

One really really nasty way is to tell windows the PROGRAM FILES directory is on the D: partition. This would mean everything that looks for that folder will end up on the D: partition, but since you have a running environment already it will probably beak more then you want.

Reconfiguring the partitions is the best option.

You can use GPARTED live cd for this, depending on how many clients your talking about.