How do I do this, can I please have instructions from scratch.

*I will also be formatting my computer, I have a 120gig hd, Pentium 4 3.2

You will want to check the documentation for some info on this.
What I see listed on the Mandrake site is for 9.2. Generally it would be the same, but perhaps not completely. I would guess the docs are also on your install CDs. Maybe in a Docs folder?
Can any Mandrake users specify where the current 10.0 Mandrake documentation can be found on the install CDs?
The basics are, resize the Windows partition that is currently using the entire hard drive, install Linux to the free space, use either one of the Linux bootloaders or the Windows bootloader to select which operating system to boot.

If you are starting fresh on both XP and Mandrake, then start the XP installation first. Partition the 120G drive, using xxxxxG for XP and leaving the rest untouched. ( I leave at least 10G available for Mandrake, but it's your call, because it depends on what you will be doing with it ). Install XP, then when it's all done, install mandrake using the 'custom' partitioning option in the mandrake installer. Select the unused space that you didn't use during the XP installation, and make at least a '/' and a /swap partition. Then press on. Make sure you do NOT format over the windows partition on the next step. Only format the linux partitions, then continue. clear as mud!

Hope this works out for you

(SOMEONE CHECK ME ON THIS )

Windows has a nasty habit of putting information at both ends of the hard drive that can make it difficult to resize the drive.

Steps should be
1) defrag the windows drive completely using the windows defrag utility in accessories/system tools (or something like that) This will (or rather should) move all information to the beginning of the drive.

2) boot the linux install cd

3) When the partitioning comes up:
select custom partitioning

4) click on the dos partition and then click resize
Reduce the size of the windows partition 10 to 20 gigs if possible. (should be enough to get you started)

6)The new blank space should be gray. click on that
and then on the auto allocate.
Linux will sub devide the blank space automatically into a
/ partition (boot)
swap partition
and a user or home partition

Once that is done, you should be off and running.