CCleaner sometimes doesn't clean all the space used by browsing

200mb will not give you what you need if you are ever in need of a restore. 200mb < 1/3 of 1 compact disc & 1% of the required disc space just to run the operating system

Good understandable write up here on xp system restore.

Item 5 talks about how much space to allocate.

http://www.techrepublic.com/article/10-things-you-should-know-about-windows-xps-system-restore-tool/6048545