For some reason when searching things like Xen (or anything 3 letter or lower) I get no results at all?

This is due to an index limitation - words which are three characters in length or less, or words which are 'too common' cannot be used as single search queries.

Try add a tail to your query - such as "xen server"

Or failing that, use Google which has no problem with short terms:

site:webhostingtalk.com xen