Valve Software and S2 Games on Tuesday announced plans for Beta testing of their upcoming releases. Valve has a sign-up page where potential Beta testers can apply to test the Mac version of its Steam online store. Meanwhile, tomorrow S2 will open Beta testing for Heroes of Newerth, its strategy game based on the Warcraft III scenario Defense of the Ancients.

Once Steam is released, which is expected to happen in April, it will be the home for Mac versions of all of Valve’s games, including the Half-Life series and Portal. Other publishers will be able to sell Mac versions of their titles at the online store too, and Valve representative have indicated that there’s some interest in that. Valve wants potential Beta participants to answer a few questions about their gaming habits and upload their System Profiler information, so the publisher can direct the testing toward the widest spectrum of available Macs.

S2’s open Beta testing of Heroes of Newerth, which won’t require an application, is expected to commence on Wednesday, March 31. The game has been in closed Beta testing for several months now as the developer tweaks the gameplay.

Thanks to Inside Mac Games for the heads-up.