i'd agree with the nohup suggestion say if you're untarring a large file you can leave it to run on the remote server without you needing to be connected.
eg if youre running:
tar -zxvf big_file.tar.gz
then type the following in instead:
nohup tar -zxvf big_file.tar.gz &
(note the & at the end - this puts the job into the background)
alternatively you could try the screen program, not used it myself but i think it should do the job theres an excellent article here im just havin a read of myself