You should check if the service partition exists on your system. On older systems (T40) it seems to have a frre space after the system partition (If the settings of the predesktop area in bios is set to disable). If you know what is the type of your hard disk, you should see the size on the net. Newer systems (like my T42 there is a partition after the system partition.
If I were you I try to boot from CD (Hiren's boot Cd) and I could start Partition magic from the cd and I can see what is the situation on the hard drive. Before I boot, I disabled the predesktop area in bios, so it can see on the hard drive.
If this is an older-fashioned predesktop area (T40) and there is only one partiton on the hard drive and the size of this partiton is smaller than the size of the drive (size is 40gb, but only one 36gb partition exists) then you have to make changes in bios, because the predesktop area is still hidden.
If the size of the partition is the same as the size of the hard drive, then you overwritten the predesktop area. In this case I can try the Emergency recovery Pro software. Your XP were on Ntfs. You can be sure that if you only made a bigger partitinon then your files are recoverable from your hard disk. You need an USB hard drive or you have to remove the hard drive from your thinkpad and install it to a desktop computer. Start the emergency recovery pro and it will recover your files to your USB hard drive. You will find the I386, Ibmshare,Ibmtools,Drivers folders and with these folders you can make a clean install. The howto is a sticky topic in the forum.
http://forum.thinkpads.com/viewtopic.php?t=3827
If you have a newer predesktop area (like on my T42), this is a partition after the system partition. If this is exists, you can make it active and bootable in Partiton Magic, so your system can be booted from it.
If you dont have Hiren's boot cd, send me a mail and I can upload it to you.