If u use only a small space(not ur full 40GB) for ur current winXP installation,you can create partitions without formatting.
You can use winXP tool 'computer management' for it.
Right click the 'My Computer' icon and select 'manage' option.
You'll get computer management tool.
There you can create partitions.Right click on empty space and create partition.
A good practice to create only 2 BASIC partitions and an extended partition.Inside extended partition you can create any number of logical partitions.And leave some space in extended partition as unallocated if u wish to install linux later.
But if u formatted ur 40GB fully for ur current partition,u must format the partition again and install winXP again in a small space.Then goto computer management tool.
I used Partition Commander to partition my drives on Win 2000 without reformatting. Basically it "moves" your files and creates partitions in the space. It boots from a floppy and can do other stuff like resizing and changing file systems. It has wizards for partitioning to opitimize for speed, space and for booting up from other operating systems.
Quite handy and easy to use. Don't know how it compares to native XP partitioning because I've never used it. It's not free btw. [ October 07, 2004: Message edited by: Richard Hawkes ]