Hi RichardB,
that is not Quest's fault, it will most likely be down to slow proc. or I/O problems (you did say they are dev boxes).
I don't think there is much difference between SQL 2000 and 2005 with respect to using Quest/SQLBackup etc. They just use the VDI and pretend to be a tape system and consume data much faster than a tape could.
Would be interesting to see if there is much difference if you move your dev boxes to 2005.
Regards,
WilliamD