You can try setting it to 400 in bios - it may work on that mobo.
Cad can use 2gig, a couple games can use >1gig, so I'd say try 400, if not, oh well. The performance loss 400 to 333 with A64's is at most a couple % (and that only for a few apps - most are little to no difference).
What little advantages you would get from a CAD program would be completely lost by the lower speed....in fact it would proabbly run slower.
1GB of RAM....Period....even the famous BF2 which everyone thinks they need 2GB of ram for....it only gets you 2% increase. YAY 2% for $80-$130....if you spent that much more on a gpu you would get 35% increaese and if you spent that much more on a cpu you would get 5-15%