As I only have a 9.1Gb HDD I was wondering, with the few apps I have installed, where all the space had been used. Going through the directories I found my Sierra directory and sub-folders contained 2Gb of files. First off - CS1.3 has a feature whereby the end of game scoreboard can be automagically captured. This was enabled without me knowing (prolly my brother playing around with the setting) which caused nearly 1Gb of image data to be saved over the months. Also, a number of Half-Life mods - Firearms, Death Match Classic etc... were installed taking about 100Mb. I don't play them so bye bye to them. Then there is a file in the /valve directory called pak0.pak which is 100Mb alone. It contains sounds, skins and textures used in Half-Life tho' some I recognise from CS. Using Wally I deleted all the Half-Life sounds and models CS doesn't use. pak0 is now 47.2Mb.

End result: the Sierra directory is 650Mb with a backed up pak0 included in that tho' only playing all the maps will reveal if I've broken anything.