It makes so much sense for Konami to build hype (as if it needs any more) for Metal Gear Solid 4 by releasing Metal Gear Solid for the PS1 onto the PSN Store. So far, however, it's only confirmed for the Japanese market with no word on a European or American release. This is nothing new - Japan has been receiving large numbers of PS1 games twice a month since the store opened. (The last PS1 game the EU store saw was Reel Fishing. Oh dear.)
There is still hope, however. Ryan Payton, on the latest episode of the Kojima Productions Report podcast, stated that they will be gauging the response in Japan and seeing how many people download it. If interest in high then it could be released elsewhere. Considering we're putting our hopes in a nation who hates digital distribution, chances are you may want to just grab a copy of the Metal Gear Solid Essential Collection. Just in case.