A week-long beta for Darkspore opened today for PC gamers exclusively on Steam (download the Steam client here if you need it). The beta will run through noon pacific time this Friday, April 1. During that time you'll be able to play both co-op with up to four players against computer-controlled Darkspore and 1v1 or 2v2 player vs player competitively.
The email announcing the beta also confirmed Tuesday, April 26 as the Darkspore release date. Though that doesn't allow much time before the release, the developers say they plan to use what there is to "fine-tune the game, incorporating fan input, so that the game is just right when unleashed."
[UPDATE] If you plan on getting the game, you might consider teaming up with some friends. We also got an email from Valve Press with word that as a pre-purchase special a four-pack of Darkspore can be had for the price of three.