Major Problem Key Partitions MIA

So I my computer wont boot up. It gets to the CD stage and asks for the OS disk which I provide. I get to the install OS section and there are no partitions and about 70meg of space left. This is VERY worrying as I have two partitions, one with the OS on and one with critical unbacked up [long story] data. I dont give a straw about the os, but I must retrieve the missing data from the second partition which did not have the OS on. What are my options? How can I make the comptuer see the partitions long enough to reinstall the OS and get the data back?

 

Forgot to add, using XP Pro.

 

Right, so I have set the drive as a slave to another drive with os, and run a few partition programs. It just keeps telling that there is 32 gb unallocated, which is rubbish given this is a 40gb drive with 20gb in use, and does not show any partitions. I really need any advice on how I can recover the lost partitions and retrieve my data.

 

Right so solutions: I have dropped a bit money and bought a new 160 gig drive and I am planning to move as much data across from the old drive using http://www.easeus.com/datarecoverywizard/index.htm So anyone out there know how I could have the same thing without shelling out lots of notes?