Ok, here is what I got for ya.
The info can be found on pages 49-64 of the SWMB Companion. It also mentions that more info on the Imp. Army can be found in the old WEG Imperial Sourcebook.
Here are the basic breakdowns.
Rebel Alliance
As a whole does not have one cohesive organization. The member worlds are free to organize their forces in whichever way they feel is best. However, the Rebellion does maintain an organized force for those times when large-scale actions are required. These forces are Alliance High Command's SpecForces. They are the forces one usually thinks of when Rebel soldiers are mentioned. These troops are also used as marines, assigned on board and guarding ships that carry important cargo. The organization of even the SpecForces is flexible, being adaptable to different situations as required.
Division = a flexible number of Regiments which task forces are assembled from
Regiment = 4 Companies
Company = 5 Platoons
Platoon = 4 Squads
Squad = 10 soldiers (incl. Commander and 1-2 specialists)
A typical Assault Company could consist of 4 Line Platoons and a Heavy Weapons Platoon.
Now I could go into much more detail for the Rebels or if you would like I could try to scan those pages as they include markings and such. There was a dealer at GenCon and Origens selling these old books at 10 for $30, well worth a look at.
Imperial System Army
Army = 4 Corps (Line, Atrisian, Armor and Mobile)
Corps = 4-5 Battle Groups
Battle Group = 4 Regiments
Regiment = 4 Battalions
Battalion = 4 Companies (close in size to a Rebel Regiment, and varies in size depending on type)
Company = up to 4 Platoons
Platoon = Lt., Sgt. Maj., 4 Squads
Squad = 8 Soldiers
The smallest independent unit was the Platoon until after Endor at which point the Squad became the smallest independent unit.
Stormtroopers Organization
Emperor
Corp Commanders
Stormtrooper Corps = 4 Divisions
Division = 4 Brigades
Brigade = 4 Battalions (equivilant to the Imp. Army's regiment)
Battalion = 3 Companies
Company = 4 Platoons
Platoon = 4 Squads
Squad = 8 or 10 Troopers depending on mission (including Sqd. Commander and possibly some specialists)
The squad is the smallest independent unit.
Now I don't know how canonical that is. I see in the old WEG SW Sourcebook they list a Standard Battalion Garrison as having 800 Stormtroopers. However, using the SWMB Companion you would have 480 Stormtroopers max in a Trooper Battalion so there seems to be a bit of discrepancy unless there is a difference between a Trooper Battalion and an Standard Battalion Garrison.
Standard Battalion Garrison
Personnel
Stormtroopers 800
Scout Troopers 40
Speeder Bike Techs 10
Tie fighter pilots 40
Ground Crew Techs 60
Controllers 25
Sensor Techs 25
Gunners/Weapons Techs 100
Walker Crew 50
Walker Techs 80
Imp. Intel Officers 50
Base Security/detention Troops 150
Perimeter Support Troops 200
Trade Mission/Diplomats 70
Support/Services 500
Technical Personnel 200
Science 200
Medical 100
total 3000
Vehicles
Tie Fighters 40
AT-AT 10
AT-ST 10
Speeder Bikes 40
Landspeeders 60
Misc. vehicles 100
total 260
I hope this helps. I tend to use the info from the SWMB Companion for my games.