Here is the difference:
Dirty Pages: Data that has been modified and Stored in the buffer cache and has not yet been written in to the hard disk. (Transaction Logs)
Dirty reads: Reading the data that is actually read by Transaction2 which was modified by Transaction 1 and Transaction1 was not yet committed and above that, if Transaction 1 is rolled back then transaction2 has read data that never was modified or exists... This is dirty read.