Do you mind loosing all the information on the drive in which you will reformat?
If you DO NOT want to loose any data (2 options)
opt:1--Backup data, then proceed to options 2
opt:2--Use a program like partition magic to merge it within windows (will not loose any information)
If you don't mind loosing the data (2 options)
opt:1--If using winxp... click start, go to control panels, administrative tools, computer management. under Storage the is a "Disk Managment".. Click it and find the drive with the 2 partition you wish to merge. (be cautious) C: is your main drive.. do not reformat that one... D is probably the dirve letter to look for. Delete both partitions and then format the entire thing (right click)
Good Luck!