IMP NOTE: The following procedure involves formating, partitioning your Harddisk. Do not forget to take a backup of your data before proceeding.
SOURCE & CREDIT - WinVista Club
You may not need to have 3rd Party Softwares to achieve resize partitions in Windows Vista.
Try the following steps -
Right Click on Computer - Manage
In the left pane, under Storage category, click on Disk Management
Now select and right click on the partition you wish to modify.
In the context menu, you will see options to Extend, Shrink or Delete the partition. Select the option you want.
You can not merge partitions in Vista with its Utility. If your 2nd partition is empty, you can delete the 2nd partition and then extend the 1st partition, to use the freed up space.
Also note that you can extend only to the right; if you are desirous of extending the partition to the left, you may have to use a 3rd party utility, like Acronis.
Sometimes one or more options may be grayed out and thus unavailable. It could be that such a step may be physically not possible.
How To Resize A Partition In Vista, if Disk Management fails.
Should you wish to continue, nevertheless, please first backup your important data should anything go wrong. You may have to use diskpart.exe ! Diskpart utility can do everything that the Disk Management console can do, and more! It’s invaluable for script writers or anyone who simply prefers working at a command prompt. For more information on it click