Partimage over a network and restoring them

[creeds]

Hello,
I found partiamge quite useful for backing upo a whole partitions ans restoring them , and also found that it can be done over in a network.but problem is that of unmount the partitions.
how can i umnount partitions like /var or /usr which is not unmonunted with that ease, it always says the device is too busy.so how can i proceed.
Also, does restoring needs to have same type of system, or same hardware configuration?
any suggestion reagrding this and other issue of partimage will be highly appreciable,
with regards,
Creeds......................