If you just want an estimate of intrasubject variability, not accounting for other variables, just put in subject as a random factor. That would be your only independent variable. Your DV is whatever you want the variability for.
You'll have to use a mixed models procedure--Proc MIXED in SAS, Mixed Models in SPSS, etc.
If you tell me which software you're using, I can tell you how to do it (depending on which one you use).