Can I upgrade from snow leopard to lion even though mountain lion is only available?

You might be able to find a Mac OS X Lion preloaded USB thumbdrive at a second hand store such as ebay, Amazon, or a classified site like craigslist. Unfortunately, there's no more digital downloads officially available from Apple's App Store anymore.

EDIT: There's no way you can run Lion without illegal hacks, let alone Mountain Lion on a Core 1 Duo iMac.The highest OS your Mac is able to run is Snow Leopard officially. If you insist on hacks to run Lion on a 32 bit Intel Core 1 Duo iMac, you can follow up here: http://www.youtube.com/watch?v=346qmgjBI6c

I don't think you can use those same hacks for Mountain Lion though but even if you got Lion working on it, at least you will have some longer life out of your older Mac. If you insist to get either of those running on your iMac, I would still buy either of those OS's though. This is just for educational purposes and I will not be held responsible if something goes wrong with your iMac.

See thread for one example about not being able to upgrade to Lion officially: https://discussions.apple.com/thread/4274829?start...

in case your iMac has a minimum of 4GB of RAM, purchase Lion now. it's going to be swifter in use than OS 10.6, even with the actual undeniable actuality that slower to start up. you could not get it from the App save, because Apple in user-friendly terms supplies the present, OS 10.8. you should call i-800-myapple and ask to purchase it. all the extra reason to get OS 10.7 previously it truly is lengthy gone always. in case you purchase it, you could deploy it or no longer, yet basically purchase it. in case you want to position in OS 10.7 and observe the way you want it, you should use Disk application to make a 2d partition, and deploy it there. See the link decrease than for an party of triple-boot Lion / Snow Leopard / domicile windows 7.

For some odd reason, Apple doesn't seem to sell older versions of its software. Your best bet is to find it on ebay.