There is an excellent program available for this called "partition magic." It is pretty much the only way to re-size partitions without having to format & thus losing the data. Its not free, but it is pretty cheap for as good as it is.
The link below will take you to a list of freeware & shareware programs which also may be able to help. But remember, when working with partitions tread carefully, one wrong click and its all gone.
Incorrect: While partition magic will do what you want it is by no means the best nor is it the only option. The best and free option is to download almost any of the Linux live CD's and use their program called g partition. Don't be afraid of this because it is "Linux". It is just as easy to use as windows, I swear. There is even a special Linux that only has g-parted on it, it is extremely small and can run from a usb drive or live CD. G-parted is better because the hard drive in question does not even have to be bootable in order to use it, plus it is free. Also it can format into both NTFS and Fat plus the Linux formats so you can use it to make drives for Mac or Windows. It is awesome check it out.
The area on the hard drive that contains a map to all the partition on the drive is called the partition table. That is what partition utilities edit when you add, delete, convert, or resize a partition.
The system partition(a partition where the operating system is installed) is the active partition of the Hard Drive
Unless you already have a free partition on your hard drive or an additional hard drive, you cannot install Red Hat Enterprise Linux without "disturbing" Windows; you will need to resize the Windows partition to make room.
system partition
System partition
Most of the time the boot partition and the system partition are the same partition on the drive C.
extended partition
Most of the time the boot partition and the system partition are the same partition on the drive C.
By default C: is the active partition of the hard disk drive
Your question isn't exactly clear. If you want to install Ubuntu natively onto a partition, you must format the partition or make a new one. It is quite possible to resize the XP partition and make a new one without losing data on the XP partition. Ubuntu already includes the tools to do this.
active partition
You just partition the Hard drive not the RAM.