How can i ignore case

I have 2 excel sheets that hold information that have a common cell.

What i am doing is comparing one cell to all cells in the other sheet. The aim is ro find if a file has been uplaoded.

But for some reason some filenames have weird charcters and are lower case. This isnt the same for all.

Example:
Excel Sheet 1:
thisFileName.jpg
thisIsOrig/Aye.jpg
This is also.jpg
Here.Is.A.Nother.One-CF.jpg

This are similar filenames that the second sheet has, the one i check with.
These are the filenames in the sheet that i am checking against.
(They also have the weird characters in the filename next to it)

Excel Sheet2
thisFileName.jpg >>> this is ok and can be seem as correct
thisIsOrig=Aye.jpg >>> this is wrong, / has been changed to =, but sometimes / is kept in
This_is_also.jpg >>> This is also wrong, spaces shouldnt be _
Here.Is.A.Nother.One-cf.jpg >>> this is wrong as case has changed, although case doesnt always change.

I have a fait idea that i can use Ifs to look for the =. But i dontknow how to make the case be ignored.

Any ideas?

have searched but didnt find anything

hth
http://developer.apple.com/documentation/AppleScript/Conceptual/AppleScriptLangGuide/AppleScript.c8.html