Office Program Startup Issues

I am having issues with Office 2003 products. I have Word and Excel on my computer that I use frequently. Whenever I try to open either file this Windows installer comes up and says its "preparing to install" then a bar starts to fill up on the screen (a loading bar). when its full it goes to this screen that says
"Installation Error; File not found:
A required installation file: YI561403.CAB could not be found.
Other times it mentions another file but I have not written it down yet.

I do not have the disk to put it like its asking me to do. What do I do?

Unless I click cancel a bunch of times as this screen pops up, it will not even open Word or Excel. And If I try to open a file by double clicking it (with word NOT open) it does this aforementioned process and will not open the file but instead open word with only a blank document or sometimes no document at all opened up.

However, if word is ALREADY OPEN and I double click a file somewhere (like an icon on the desktop) it will open fine with no errors.

anythoughts?