Is everything up and running fine since you reinstalled?
If so, go ahead and trash the previous system folder.
BTW, in case you've not done it before:
QUOTE
Delete the Previous Systems folder from a prior Archive and Install
If you have performed an Archive and Install of Mac OS X, a Previous Systems folder was created containing your prior Mac OS X System folder. Once you are satisfied that your Mac is functioning properly after an Archive and Install, you can delete the Previous Systems folder as follows:
Mac OS X 10.3 Panther® or later:
Using your Admin account, drag the Previous Systems folder to the Trash.
Type your Admin password when requested to authenticate this operation.
Empty the Trash.
Mac OS X 10.2 Jaguar: See the AppleCare Knowledge Base document "Mac OS X 10.2: How to Delete a Previous Systems Folder."
http://www.thexlab.com/faqs/freeingspace.html