[tbaher]

Compression (with or without "full functionality") ratios depend largely on what you are compressing. Nevermind the different algorithms/programs, some content just compresses better than others. Like if a game has a folder with 400 MB of wave files for instance or BMP files or just plain text, there is gonna be good ratios. The problem with today's games is that they already come on multiple CDs, and so I assume (since this IS 2004) that most of these games have MP3s, etc instead of audio tracks and compressed-to-all-heck textures, etc. and I'm just talking about the ones that run off of the CDs.
Things that run off of the hard drive with the CD only used for copy protection usually have everything ultra-compressed and then unloads all of that content on the hard drive (anyone seen Armed and Dangerous's install footprint? 3GB for a 2 CD game, or so i heard) but I digress.

Bottom line, Farstone Virtual Drive (to name one - one that stinks at 1:1 copies no-less) lets you compress the image files you make, but the ratio is so variable that you could be saving 10 MB or 400 MB.
To get this 400 MB though you have to have a CD that is very compressable (games that have regular-AVIs for FMV and BMPs/TGAs for textures)

Forget about the 20 CDs that are compressed down to 235 MB to fit in a 4.7 GB DVD-R

/rant

Buy an extra 120 GB hard drive or two and you won't have to worry about fetching CDs (assuming you WERE willing to get cracks for all your original games) or worry about that dodgy drive (like my creative crap dvd) that won't read a lot of CDs without spitting them out a few times.

/bad advice