Format the drive or partition with Linux on it from within Windows.  Right click on My Computer and go to Manage, under Storage click Disk Management, then right click on the drive or partition with Linux on it and select format.  If you had seperate partitions they will stay seperate but you will have the space back.  If you want to merge the partition back with the main drive you will need a program like Partition Magic, http://www.symantec.com/region/au_nz/product/partitionmagic/features.html