It is a long time since I installed Photoshop 7.0 (circa 2003!) but if I remember correctly, do you not get an option to enter the previous version serial number, if the old version is not detected?
Note : You may have other problems with Photoshop 7.0 on a new system. For example it will not recognise disk partitions greater than 1TB (they simply were not fitted to PCs back in 2003)
Thanks, Dave! Oh, I wish it did have that exact option but I've not seen it. Upon running the installer, it will allow the options of Search hard drives for prior installation, Search a specific location for prior installation, and Very original Photoshop media. Once, I thought that third option would get me going, but then it rained on my parade. To verify the media (which would be the 5.0 version in this case), it requires the insertion of the 5.0 CD. Well... guess what. No DVD drive on this newest machine. With so much use of Flash drive, I opted to leave the DVD player behind on this one and it won't accept/recognize the flash drive for this purpose, and does not allow the user to select where to look for the files (else I could direct it to the Flash drive or the hard drive). It auto-looks for a CD. For installation purposes, I had copied files from CD to Flash (using another machine) and then to the hard drive of this one. Each option to get going hits a road block. 5.0 is too old to install which prevents the 7.0 upgrade installation, and I can't verify the 5.0 media because of no CD/DVD drive.
An external USB DVD drive costs around $25-$35. Perhaps it might also work to copy all the Photoshop 5 DVD contents to the ROOT of a usb flash drive, and insert that: it should show up as a drive which Photoshop 7 ought to recognize as an installation/DVD drive.
Great ideas! Your putting the 5.0 files in the ROOT of the flash drive idea gave me real hope, but unfortunately didn't work. The system seems to only want to recognize what it considers a CD drive. I may have to try your suggestion of the external - assuming that the system will accept an external for recognition purposes.