I stumbled across this little tip in the MS Knowledge Base today:

...the following line of VBScript forces an immediate garbage collection:

Y = len(string(65537, 'x'))

This script line fills up a temporary string larger than 128K, which causes garbage collection to start. The temporary string is not stored; if it were, the string contents would not be freed until the aforementioned conditions are met and the next garbage collection is performed.