A lot of users have been asking me this question lately so I decided to answer it right here. First off, I made a big error by not including the CUE files with our PAL PSX ISOs. This resulted in a lot of confusion since people were unable to mount/write their discs for playing/burning. Well, you'll now find that every PAL PSX ISO page has a link to a bunch of CUE sheets and SBI files. (needed for playing encrypted titles)
So how to use them ? Well, it's pretty simple. If you're using a single track PSX ISO, then all you need to do is unECM it (using the program provided on every PSX ISO Download page) and then mount it/burn it for use with your favorite emulator. (pSX or ePSXe)
If you download a multi-track game then things get a little more complicated. What you need to do is download and extract the CUE sheet for the ISO provided. Then, install Daemon's Tools as right now I don't think any emulator directly supports multi-track ISO files. Mount the CUE sheet of the game as a virtual drive in Daemon's Tools. (the CUE should be in the same directory as the other BIN files) Don't forget to unECM the BIN file beforehand.
Now, you can choose one of two things. Either burn the 'virtual disc' to a CD by doing a 1:1 copy in your favorite burning software. OR, use your favorite emulator to play the title by choosing 'Run Disc' and making sure that your CD drive letter in the CD plugin of the emulator and the virtual drive letter that Daemon's tools has set are the same.
That's all there is to it, really. Have fun! Questions and comments can be made as a response to this news post : ) We'd be happy to help!
Oh, and for a seriously awesome collection of Playstation ISO Downloads, check out our Playstation ISOs Section (3618 titles and counting).