I've got a little tip for those of you lucky enough to get your hands on the Windows 7 RTM iso from Technet/MSDN:
You can create your own "universal" ISO that prompts you for which of the available editions you want to install.
That's right, there is no need to download each of the different editions, the ISOs are pretty much identical except for one small file that governs which installation routine is executed when the installation runs.
The file ei.cfg, located in the /sources directory of the ISO, contains the information that the Windows 7 setup reads to kickstart the installation. If you remove the file from the ISO itself, before mounting it or burning it to a DVD, the result is that the seup prompts you for which installation you want to run and you can chose between Starter, Home Basic, Home Premium, Professional or Ultimate.
It's really that easy, but if you don't want to start editing or removing files manually from the ISO, check out Windows 7 ISO Image Edition Switcher, a set of tools that automates this little job for you.
For more details on ei.cfg check out the Windows Setup Installation Process article on Technet.