External hard drives - the basics?

Yes I have a new computer there but I want to be able to access everything on my current hard drive.  DH'd friend built our computer so he is kinda techy but I want to make sure I travel with it in the right case and then figure out the rest when I get there.

I have a Dell Dimension E510

I have a Dell Dimension E510

Three and a half inch drive.

 

I've been trying to reinstall my OP (Windows XP) but I keep getting an error message, that my Windows Installer is not functioning properly.  (Error 1722) 

Dell didn't send me a CD when I bought my laptop - so I've been accessing the Windows i385 folder EXE file.  Looked up on how to remedy error messages and tried all I were straightforward. 

I downloaded a 'recent' version of Windows Installer but still got the same error message.  Honestly I can't find the file to see what version number I had or if it was really updated.

Seriously, I've spent ALL day on this.  It's making me mental. 

So I've been looking for a way to fix my installer.  I've upgraded.  Can't find the ''Windows installer clean up utility".

I'm ready to buy Windows 7, but I don't want to if I don't have to. 

Recommendations?   

Nevermind y'all, got it sorted.

Spend almost two days hunting before I thought to go to the Dell site.  Within 10 minutes I was back on track.   

If I had reinstalled my OP a few years ago, I would have saved myself a lot of time and frustration.   

But now I know!  So thanks for the help.