Hello,
I was wondering is it possible to import a current site into Mysource Matrix, or do I have to do the pages individually?
The reason I ask is I have 300+ pages on an old server, and i've just put Matrix on a new server, and want to transfer the site across.
That depends on how your old site is stored. With only 300 pages, it would probably be easier to migrate the system manually. We usually only look at automated migration for sites over 2000 pages. 
Oh ok. Is there anywhere in the Matrix manuals I can read up on migration for large sites?
No -- any large site migration is done as a project between Squiz and the client, as every large site is different. To make your life easier, you should look at the bulk file migration tool. Also, if you are a Squiz client and have the SSV version, you also have additional import tools that can mass-create pages for you from HTML sources. Its best to speak to your Squiz Project Manager and implementation team about using these tools.