Make BartPE diagnostic boot CD: http://www.nu2.nu/pebuilder/
The A43 file manager will allow you to read/write (delete) files from your
hard drive. Look in C:\Documents and Settings\Your Name\Local Settings\Temp
for files to delete and other Temp directories too. Delete old system
restore points.
Or you could buy new hard drive and use Ghost or Drive Image to get files
that way.