Believe me, if you are asking this question, you don't want to do this manually. I have tried many times and with different OS's and ending up need to completely reinstall the software. Not to discourage you from learning, but if that is the road you want to go down, good luck.
For me in your situation, I would download the ISO for windows 7, burn it to a disk or flash drive, boot to the new creation, press F8 -> startup repair. from there follow the instructions on the screen. The utility will seek out all installations of windows of various versions and add them to the boot menu.
It may be possible that you will be asked to activate win xp again. that shouldn't be a problem though as long as you have the 25 character key.
below is a link to download windows 7 pro 32 bit edition ISO.
Nothing is ease anymore with Win 7. If I use the ISO I will have to reload all the manufacture software that came with my new PC e.g. MS Off, Trend Micro all my tools (Asus) and if something were not to work later I would have no warranty do to that fact that I reinstall Win7
Sorry John for the delay in getting back with you.
Don't use the iso to actually install windows 7 again. Only use the disk for the startup repair utilities contained there. When you boot the flashdrive or DVD you will have the opportunity to choose to repair your computer. Within the repair utilities you will have a repair startup selection. choose that. The utility will scan your hard disks and partitions for existing windows installations. Without installing or reinstalling windows the repair utility will in normal cases add all found installations to the os boot screen where you can choose either win7 or xp. The names of the choices may not exactly state XP etc. you may have to click and see. Once all is operational, from windows 7 you can edit the os choice names and default os to be booted after the preset timeout.