sp2.1 slow sketch performance

after installing sp2.1 i get really slow sketch performance.

If my mouse highlights a sketch line processor usage goes up to 25%( quad core, maxing out one core) once un highlighted cpu goes backto normal.

anyone else having this problem?

SW 2009 x64 sp2.1
windows xp 64
nvidia quadro fx 3450\\4000
6gb ddr3 ram
intel q6600 ~2.5 ghzSolidworksAdministration