Other problems could be from poor programming practices in your user interface. For instance, I'l bet SQLBill doesn't have many queries using cursors trying to manipulate his many gigabyte database. Cursors often look fine in a development environment with limited records, but very quickly turn out to be very slow once you are in production. His SPs probably never return more data than they absolutely have to either.
Other problems could be: network issues, a computer which is not robust enough to support the number and type of connections, lack of space onthe hard drive due to not backing up the transaction log and a whole host of ther problems.
Christy, personal edition is not sold separately, you have to buy the standard edition of SQL Server. Yes, it's expensive, but that's what you need if you are going to have millions of records. Enterprise would be even better. Also I would not use an Access front end if I were processing millions of records.