Well, just guessing it's a Dell Inspiron 1501, here is a link to the manual. It shows you how to disassemble the laptop.
To clean the fan, the best tool is a small unused paint brush less than 1 inch wide. It gets down under fan blades well. Can also use canned air to blow the fan out, just prevent the fan blade from turning as you blow air in it.
ftp://ftp.dell.com/Manuals/all-products/esuprt_laptop/esuprt_inspiron_laptop/inspiron-1501_owner's%20manual_en-us.pdf
Good Luck!!!