Well, unless you own 2 licenses I think that's against the license agreement, isn't it?
You could turn on the Instant Web Publishing (File / Sharing...) Then your coworker can see the DB in a browser window. I've used it and it's really quite easy to set up.
I have the same problem with "invalid checksum" - but I DO have two licences......
You have Filemaker 10, your colleage has Filemaker 8. If sharing is your only goal....
If you open a database in 10, have sharing turned on, she will be able to open the database.
There are some FMP 10 specific features they will not be able to access, but the database will essentially work
Are you instaling from a disk?
That error message could be caused by something as simple as a finger print or scratch on the disk. If that's possible, try carefully cleaning your disk and trying again. (The licensing issues shouldn't keep filemaker from installing. They'll just keep the two installations from sharing a file unless you use separate install codes or a code with more than one "seat" to it.)