What is it you're after exactly, Linux files for BF2142 1.51?
Oh, sorry, you're the original poster in this thread (got you mixed up with the guy from =SBB=). You should be able to play First Strike fine. If you updated to 1.51 and still couldn't get on the Rebel Defiance server, that may have been because it was set up for testing. Sometimes we switch it from the current public version of First Strike to a testing version with which we can perform testing sessions with new currently in development content. That is most likely what happened when you tried to get on the server. Give it another go.
With =SBB= unfortunately they're having problems updating as they're waiting for a Linux version of the BF2142 server files I believe. Once they come out they should be able to bring their server back up to date and you'll be able to play there too.
So in short, yes, you should be able to play First Strike.
Hope that clears things up for you.