I am planning to buy a backup tape device. I need to back up regularly. Does anyone have any experience with USB backup like seagate tapestore USB 20 gb tape backup.
Also if need to have a scscii based one what all the things I need.

USB devices are OK until you come to restore the backup - you can't do it from DOS so you'll have to reinstall Windows first.
SCSI is better in this respect, although you'll need a SCSI adapter in your PC. Probably your best bet for professional-quality backup is a DDS-3 or DDS-4 tape drive with a good SCSI adapter, but that'll be expensive.
Alternatively, use DriveImage (see the Utilities section on this site) and copy your entire partition to a second hard drive.
Alex