As for a free download with a 100mb file size, I couldn't find any reliable sources that offer the full game for free with such a small file size. It's unlikely that a complete game like Grand Theft Auto: San Andreas would be available for download with a file size that small.
You're looking for a report on downloading Grand Theft Auto: San Andreas for the PSP, specifically a free download with a 100mb file size. Here's what I found: Gta San Andreas Psp Download Free 100mb
If you're interested in playing Grand Theft Auto: San Andreas on your PSP, consider purchasing the game from the official PlayStation Store or other reputable online stores. This ensures you receive a complete, legitimate copy of the game. As for a free download with a 100mb