Is it possible for my hardrive in my desktop to be used as an external for my laptop and boot up from it?

Yes, but the question is why on earth would you want to add that level of complexity. Disk is cheap.

I’m living miles away from my desktop and want to use my desktop not this laptop as it’s not even mine

It is easy if the BIOS in the desktop supports it. Most do, but I’ve seen enough oddballs that don’t that I feel it necessary to warn you that it isn’t 100% guaranteed to work. Off the top of my head, I’d say that there is a 95% chance it will work but you’ll probably have to go into the BIOS and change the boot order.

Possible, yes but not remotely practical, and I don’t think that the owner of that laptop will love you tinkering with their BIOS settings.

Seems like this is exactly the kind of situation that remote computing products are made for, like GoToMyPC. Though it does cost money, it’s a pretty foolproof and good tool to have, adn probably worth the money if it’s really important.

If you’re only looking for files and not necessarily apps, you could grab a dropbox account, and just sync your folder with the cloud with all the files you need and just access them from the laptop through the web based interface.

Now that I am at home and have time to think about it a bit more, I just realized that a new hard drive is probably cheaper than an external enclosure. For that matter, a used computer doesn’t cost much; my buddy picked up a used laptop with passable specs for about $100.

My wife often tells me that just because I can do something, that doesn’t mean that it’s a good idea. Ask her and she’ll tell yo uI am full of bad ideas too! I think that holds true here as well.