When you deleted the partition, you probably changed the partition where Win 7 was located, so the boot menu points to the wrong place. I am assuming you still have a boot menu, since it sounds like you do.
In order to fix it, you could easily boot to the Win 7 Install DVD and use the Command Prompt to use bcdedit. You might be able to use bootrec.exe /rebuildbcd to fix the problem. But the Partition would have to be changed from whatever it was to whatever it is.
If you are not into using command line utilities, you can do as Super Sarge suggested and get that utility. I believe it cost some money.
The alternative, EasyBCD, is a good, free utility but requires some extra stuff to run in XP. It should state the requirements on the NeoSmart Technlogies website.
Or, you could add the partition back to see if that would allow you to boot into Win 7.