System Restore won't delete any of your letters, e-mails, or other data files, thank goodness. The files you created yesterday will still be there, even if you use a Restore Point from last month.
Since System Restore only deals with Windows XP's settings, it only helps with Windows XP itself. It can't help you locate deleted e-mails or recover deleted files that are no longer in the Recycle Bin.
Using System Restore to "go back in time" won't disinfect your computer of a newly acquired virus, unfortunately.
If you use a Restore Point from two weeks ago, then any programs installed since then might not work. Programs often alter Windows XP's settings as a way of introducing themselves to your computer. When Windows XP "wakes up" with settings from two weeks ago, it won't remember that those programs have been installed. You'll probably have to reinstall them.
System Restore normally takes a "snapshot" of your computer's most treasured settings every day. However, storing all these settings consumes considerable amounts of space. If the available hard disk space on your C drive runs lower than 200MB, System Restore stops working until you clear off more space for it to store its settings.
Also, since System Restore has a limited amount of storage space, it deletes its oldest Restore Points to make room for the newest. That means your "window" of available Restore Points might be as little as two weeks into the past.
