Here you can download some usefull software tools to help you manage a ROM collection. A renaming utility will save you time, and more importantly, it will identify bad ROMs. Consult the documentation included for further information. What these do is convert known bad ROMs into known good ROMs , by appplying a small patch file using a patching utility. Instructions are included with the installer.
BETA version adds Zipped ROM support.
This tiny utility can swap the byte order of a ROM between all three possible formats, and give it the correct file extension. Another advantage of Byteswapper is that it can report the current format of a ROM without making any changes. Beware though, it is buggy - Byteswapper sometimes renames files wrongly, either messing up the prefix or not changing the extension. So after using it, you must check the file, and if necessary rename it by hand. Luckily it always seems to perform the actual byte-swapping correctly.