You've done half the job already. First a few "ground rules" on extending partitions.
1. Most recent versions of Windows will allow you to EXTEND a partition - that is, to add to it some Unallocated Space - as long as that space is CONTIGUOUS with the existing Partition. That is, the Unallocated Space MUST be right AFTER the Partition - not somewhere else on the disk, and not before the Partition you want to extend.
2. The Unallocated Space to be added also must be contiguous - it cannot be in two blocks separated by some other Partition in between them. If that is the case, only the Unallocated Space right after the Partition will be added.
3. Up to and including Windows XP, Windows itself will NOT allow this operation on a Boot Partition, and will not allow it on the partition that has the paging file (usually located on the same disk as your OS). VISTA can do this operation. But it still might be advisable to temporarily get rid of the paging file, then re-establish it after the expansion is complete.
4. So, IF you are using Vista or Win 7, and IF the Unallocated Space you have created is right AFTER the boot Partition you want to extend, you're in good shape.
Here is the process for one drive. Apparently you already know how to get to Disk Management. Go there, then RIGHT-click on the existing main Partition. The resulting menu should give you the option to EXTEND that Partition into the Unallocated Space. Since you want all of your drive to be in that one partition, just set it to use up all the space.
If you get an error message that says anything about the paging file, here's how to get rid of it and re-establish later. Windows keeps this several layers down in menus to avoid having users change it by mistake. Windows WILL work without a paging file, but more slowly because this file is really important for memory management with large data files.
Click on Start ... Control Panel ... System, and choose the "Advanced" tab. In the first part, "Performance", click on the "Settings" button and choose the "Advanced" tab. Near the bottom under "Virtual Memory" click on the "Change" button. You will see your current settings. WRITE THESE DOWN so you can re-create them! Now choose the "No paging file" option and click OK. Windows will give you dire warnings but you can confirm your actions and back out of all these menus. You must REBOOT to make this happen. Now you have NO paging file and you can proceed to Extend your boot Partition.
When you have finished the extending and rebooted, go back into the Paging file setups (as above) and restore the original settings about where and how large it is, and whether it is custom or system-managed size. Hit OK, confirm your choices, back out and reboot. Your paging file should have been restored, and your disk Partitions should now be the way you want them.
NOTE: If you are working with Win XP or earlier, you cannot use Windows' tools to extend the Boot Partition. You CAN do this, however, using third-party Partition Management software. Usually you'd have to buy it, but there may be some freeware for this, too. Check out Partition Magic or Acronis Disk Director, among others.