What level of experience do you have with UNIX? as an end-user or an admin.? "The Linux System Administrator's Guide" from http://tldp.org/guides.html
can be a good start.
When comparing Linux and UNIX, I think it is like comparing Solaris and HP-UX. There will be some new things to learn, but not a lot. For example, if you are a RH user, you need to learn rpm.