Docs to Go is an app that includes Word to Go, Sheet to Go and Slideshow to Go which are the equivalents of MS Word, Excel and Powerpoint so that you can view docs on your BB.
In order for Sheet to Go to show up, you'll need to register Docs to Go.
As for what 4.5 OS you should download, check the OS 4.5 forums for the most recent official release for the 8330. Since I upgraded to a BOLD, I've lost track of the version history for the Curves.
Good luck on the upgrade tomorrow! I have some links in my signature that may help you out.
I can tell you just follow the tips in the Sticky and back up everything... also get the latest DM from BB before you do the upgrade... then make sure you let it upgrade do not unplug till the DM says all done and you click finish and dm is back to normal... that way you don't Brick it... good luck