Stuff happens. It just happens just so that this time I accidently mistaked my backup partition for another partition.

The partition was in the beginning of the drive and was formated to ReiserFS. How can I recover it? Surely its possible and perhaps simple??

If it was a Windows partition then I would be sweating right now. I had some important documents on there and would strongly prefer not to lose them. However I have faith in the Linux community and I hope that they something up their sleeves for dumb mistakes like mine.

Umount the partition NOW! Stop the possibility of writing to that partition and over-writing files.

Others Linux users with more information will respond; just protect that partition by umounting it until you have information to work with.

I deleted the partition using m$ windoze XP. What my next step?

Note: I didnt format the partition just deleted it.

testdisk from a Linux liveCD - Knoppix has it I think.

you cannot recover ext3 partition
is it ext2?

Nuff said. ReiserFS

????.
Nothing to do with it.
Deleting a partition (using normal means) is merely deleting the partition table entry. This only defines the start and extent (sector count) of the partition.
No data is touched, and the filesystem is irrelevant. Yes, ignore the comment above - we are not talking filesystem recovery here, merely part table entries.

testdisk.
Or if you are sure of your sizing, just add a new partition of the same size from fdisk. Works fine.

One last thing: If the new partition is roughly maybe one or two megs off or say a few bytes off it shouldn't matter?? It should have any extra since its in the beginning and the second partition is still there.

Also if I add a new partition through fdisk how do I define the partition type??

It's the beginning that counts - size is only of concern if you have filled it completely with data.
Very unlikely.

I know that there are tools which can search a disk to look for partitions... the contents of various types of filesystem labels are fairly well known.

It's a good idea .. a little late to mention it now, perhaps .. to print the partition-table of a disk to a file, and store it in the root directory of the first partition of that disk. (And in a nice filing-cabinet...)