If the workunit is still assigned to you there is no problem with finishing it on another computer. GIMPS and PrimeNet will credtit the work to you.
To find out if the work is still assigned to you you should look to your personnal status pages
http://mersenne.org/cgi-bin/primenet...&UserPW=xxxxxx (assuming you use version 4 of PrimeNet) where you replace xxxxxx by your user ID and password, if you do not remember them, they are in the prime.ini (assuming you are using Prime95 V24.)
You could also search for the exponent in the general v4 status page found here
http://www.mersenne.org/primenet/status.shtml in the
Hourly World Test Status, Assignments Report.
Jacob