Adjusting System Restore values

The new System Restore feature in Windows XP automatically backs up a snapshot of your system, including your Registry, every 24 hours. It also saves restore points for 90 days. Neither of these values is directly editable in the System Restore program, but you can change them in the Registry. Go to:

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsNTCurrentVersionSystemRestore

You?ll find an assortment of settings here. To change the interval between automatically created restore points, change the RPGlobalInterval setting. To change the number of days that a restore point is retained, change the RPLifeInterval setting.

System Restore time intervals are measured in seconds, not days, so you must convert the number of days you want into seconds. There are 86,400 seconds in a day, so multiply 86,400 by the number of days you want to determine the value. (There are 3,600 seconds in an hour, I hope you know)

source:here