I have removed your serial number and mailing address from your public forum message. Unfortunately I am unable to provide any solutions to work around needing to install Photoshop 6 with the requirement of Photoshop 4.
What are the specifics on your computer? Perhaps we can recommend a current product which might meet your needs?
Those old versions don't actually need the discs, they just need the serial from somewhere. On Windows that would be the PS 4 info stored in the Registry, which actually was just the unencrypted serial with some otehr stuff. The specific formatting was different between versions, though. The keys were stored somewhere in HKEY_Local_Machine\Software\Adobe and so on. Maybe some web search will turn up the info you need somewhere...