Windows 7 beta seems to be very solid without many bugs and what is so impressive is that it runs quite well on very slow computers. For a well written guide how to download and install Windows 7 beta read this guide at Gizmodo.
For my Windows 7 installation on my Eeepc 900, I have found that there are two major things to do which speeds up the OS further.
1) Change main Windows 7 theme to any of the lighter “simple style” themes. There is a “simple style” theme which looks similar to the standard Windows 7 theme.
2) Use a USB memory, SD card or almost any other flash memory to boost your OS using ReadyBoost. To do this, just plug in, ie a USB memory stick, and choose ReadyBoost from the autoplay menu which pops up, the more memory you allocate, the better. Alternatively, if you have autoplay disabled, you can open explorer and right click on the memory stick, click on preferences and check out the ReadyBoost tab.
This is what I found out so far and if you know any other easy and powerful ways, let us know in the comments.
Bonusinfo: Some guidelines about how to install Windiws 7, only related to Eeepc.