Here's your manual in case you don't have it:
http://support.dell.com/support/topics/global.aspx/support/dsn/en/document?c=us&dl=false&l=en&s=gen&docid=45FAC9DF3456B193E040A68F5A285493&doclang=en&cs=
See page 82 for system setup, but I do not see any USB device listed under bootable devices in system setup. Sounds like you'll need to replace that CD drive. You need an IDE CD or DVD drive. Here are the instructions for replacing that drive:
http://support.dell.com/support/edocs/systems/dim1100/EN/SM/parts.htm#wp1088942
You should not have any trouble finding a used CD drive for under $10. Don't forget to set the drive jumper to cable select.
Here's the problem. A few months ago I tried logging in but when I did (and after the Windows XP sound played out) I soon realised nothing was happening and all I saw was my background - that's it! So now I wish to format my hard drive but the problem is my internal CD-ROM drive does not open (don't ask why - it's stuffed). So now I've plugged my external DVD-RW into my PC, inserted my Windows XP SP2 CD and wish to install Windows via that drive. The problem is I'm unsure about how to set that drive as the first priority using my Dell Dimension 1100. I need help!
Thanks in advance

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