If you are looking for a "good guide" to learn the software, you should rely on official documentation and verified archives rather than risky downloads:

I really need to install CS3 [CS3 IS DEAD] - Adobe Community

: Adobe offers a 7-day free trial of the latest version of Illustrator, which is much safer and more capable than an 18-year-old software version. System Requirements (For Older Software)

Downloading "portable" versions from third-party sites like Softfiler poses several significant risks:

For those attempting to run CS3 on legacy hardware, the original minimum requirements included: : Intel Pentium 4 Go to product viewer dialog for this item. PowerPC G4/G5 RAM : 512 MB (1 GB recommended). Storage : 2.0 GB - 2.5 GB of free space.

: These unofficial packages frequently contain hidden trackers, keyloggers, or other malicious software.

: The complete, archived Adobe Illustrator CS3 User Guide is available for free as a PDF from Adobe Support.