full sql server he can dedicate more memory than the current version can use, is that the case?
Yes, there are reasons Express is free. 2005 is 1GB RAM and 4GB storage. 2008 gives you 10GBs of storage.
Not sure who gave you the advice on not to do it. AC will say that, because they don't support or know how to support it.
No offense, and I don't know how good your IT guy/cousin is, but it isn't simple to make an instance on a different type of SQL. There are those who can, though.
