Windoze 7 is a dog, however it should be possible to setup a neat dual boot with a linux of choice considering that 500gb hard disk. Ubuntu pretty much does all the work for you from the install disk and you can then set the default as linux.
For events I don't think we need Windows, but there may be odd applications around the office where the dual boot is handy. Annoyingly there are a number of Wikipedia tools such as AWB which still need a windoze install to run.
Remember there's always my lovely puppy linux from a CD if we want to run a pre-configured reusable environment with handy open source tools that attendees could even take home with them afterwards. ;-)
I'd support buying well known laptops sold in high volume (and thus very low price for the kit you get), Asus is a good choice but I'd also look at Acer machines.
I'm surprised nobody gave us some older laptops. A couple of old slow models with a small linux install would be terribly handy at the office right now.
PS I love my small Sony screen and 3/4 keyboard, but I know many would prefer the 15 inch and the Sony's are too pricey. Oh if you are throwing away Windows 7 licenses, I'll take one thanks.
Fae