In essence all Windows folders are different.The size of the folder will vary depending on the options installed and the programs installed. The average size is about 185 - 200MB for a clean install of 98 but that is beofre you have stored data, loaded up differing programme, made downloads and so on... When a program is installed it will put files into the system folder.....The PC's temporary storage folders are in the windows folder \temp, \Temporary Internet Files etc...
You can reduce the size by deleteing the contents of the temp folder, deleting the temporary internet files and clearing the history from within Internet Options.
Currently my file is over 1 gig - but as long as the machine can cope, there is no issue.