[AccessD] SQL Server advice

After mucking around on the fringes for too long I am ready to make a more committed leap into SQL Server.  I can foresee a customer  needing to upgrade their Access back end within the next six months to a year and want to get 'expertly' ahead <vbg>.
I have a fully licenced 2000 Standard edition (acquired with an Action Pack in the days when MS New Zealand charged a one-time fee for Action Packs) on a 10-year-old WinXP box (¾GB) and I am comfortable with this at the 'play' level.

On a year-old Windows 7 box with 4GB, my question concerns which tool to use, the above ... or SQL Server 2008 R2 Express?  The downsides that I can see of Express 2008 would be (a) another learning curve (b) the nagging feeling that I remember something about these less-than-complete SQL Server implementations that is not good - like inability to do important development stuff that is available in the full-blown models.  This, iirc, was true for one of MS's implementations, long ago.  The upside is that I make the enormous leap into another century.  But wait, there's got to be more (to both -ve and +ve).

Any feedback gratefully received.   

Stephen Bond 

PS - I'm a bit like Arthur (same age and increasingly pursuing other interests), so we're not talking long-term large commitments here (financial or long learning curve).