notcorn's is NOT a solution, his would only combine data onto one partition, but not add the space from the (now empty) partition to your main-partition!
You should first make backups of all your important data on either another harddisk or burn a load of CDRs/DVDs.
Option 1) using Partition Magic or Acronis Partition expert:
- let's call the main partition A, and the other (to be deleted) partition B.
- if any programs installed on B, safe userdata, uninstall them, then re-install on A
- copy all other data over from B to A
- use the Partition program to first delete B, then enlarge A with the now free space from the former B.
Option 2) without any tools:
- Make all needed backups.
- Reinstall Windows and all your other programs after repartitioning.
If W2K or XP, you can wipe/create partitions during setup when you boot from the CD.
If W98 or ME you'll first need to use FDISK to wipe/create partitions, then FORMAT.