I need to know the difference between the empirical formulas for
oxycocone and heroin, giving also the crystaline struture of both,
noting the similarities and differences. This is in reguards to the
pain management program my girlfriend is on.

The empirical formula is the same as the actual formula:
Oxycodone - C18O3N
Heroine   - C21O5N

The two are the same in structure except for oxycodone has a methoxy
group at C3, and a ketone at C6, while heroin has a double methoxy
group (-OCOCH3) at positions 3 and 6.

The crystaline structure refers to how those molecules crystallize
together-- are you asking what crystalline shapes they will assume?
There's probably not a good answer for that. If you're trying to
distinguish between heroine and an oxycontin pill, that won't really
help you anyway since oxycontin has many excipients. Well, hope that
helps!

Sorry, I totally forgot to count the hydrogens! The CORRECT formulas
(I also forgot to count an -OH group on oxycodone) are:
C18O4NH29
C21O5NH29

Heroin gives orthorhombic plates or tablets when crystallized from
ethyl acetate, oxycodone gives long rods from alcohol. (The tautomeric
form of oxycodone gives from alcohol strongly refringent scales)

Source: The Merck Index 12th ed.