Increasing the maximum size of a .pst in Outlook 2003

The strangest thing: One of our MD’s here is running office 2003, and recently he has stopped receiving emails as he has hit the max pst capacity. I have installed office 2007 for him, although it still says “max capacity reached, please archive”. The strange thing being that his PST is less than 2gig.. he refuses to archive,and has left it to me to increase his PST’s capacity. I have tried editing the registry like so : HKEY_CURRENTUSER > SOFTWARE > MICROSOFT > OFFICE 11.0 > (here i added “PST”) . then i created a new DWORD value with a new limit for his maximum pst size.
But alas, not working!

Please advise!