Medals:

Purple Heart: Get wounded or killed in action.
Bronze Star: Get 15 kills
Silver Star: Get 20 kills
Distinguished Service Cross: Get 25 kills
Congressional Medal Of Honor: Get 30 kills

Invincibility:
Pause your game during a mission, then press L1, R2, L2, R1, Select.

All guns:
Press X, Left, Triangle, Square, X, Select at the main menu.
User Cheat by Snakeeater

All missions:
Press X, L2, Triangle, R2, Select at the main title screen.

Health:
when the title page appears press L1, R2, R1, L2, Circle, Up, L1 to start each level with health and armor which is a whole nother thing of health
User Cheat by charebare

Tom Clancy's Ghost Recon Official Website

Tom Clancy's Ghost Recon GameSpot Hands-On

Tom Clancy's Ghost Recon IGN Preview

This first-person shooter , developed by Ubisoft Shanghai, is scheduled to be released on November 30, 2004.