If you used PowerQuest's BootMagic to create the dual-boot setup you may be in for a rough ride.
In the aftermath of removing a dual-boot setup, the Hard Disk's Master Boot Record can be left corrupt. (I've had two incidences of this.)
But there is a solution with Norton Disk Doctor; with this, you can repair the MBR and go on your way rejoicing.
I now keep a boot floppy with NDD specially for this job.