internal hd won't mount

My backup/TM drive failed a while ago so I got this one to replace it. The only problem is that 2 (in 4) of the holes for the screws to mount it internally are in the wrong place. I thought about returning it, but I checked and it’s like that for every single HDD of this size or larger. I guess...

I've not been able to find this problem anywhere, so maybe someone here can help. I have a backup HD (80 Gb) on a G4 (c. 2002). It's an internal drive, and has been there since I bought the computer. It works fine. It's NOT the startup drive. But as I was transferring a file from my main...