what do you mean? winrar so that you can rar and unrar directly on-server?

it seems possible enough, it would depend who youre hosted with i think.

if youre mates with the owner of the host then they could probably install it, and if your on a public host send them an email and ask, if it can be done theyll charge you and if it cant theyll let you know.
i dont know about other servers but mine has winzip and some other compression app integrated. i use it alot. a winrar would be nice but i dont see it as a necessity.

hope this was helpful

cheers


EDIT: Check these two threads out, they directly answer youre question.

1: http://www.besthostingforums.com/showthread.php?t=6570 (how to install winrar on youre server)

2: http://www.besthostingforums.com/showthread.php?t=6720 (how to use it)

cheers