http://wiki.project1999.org/Statisti...rity_.28DEX.29
Dex shouldn't affect dual wield or double attack. They're not procs.
http://wiki.project1999.org/Dual_Wield
Not that everything on wiki is perfectly accurate, classic or even implemented on p99.
What you put your stats into depends on what you plan to do. If you are going to do a lot of raiding, you can expect you'll max strength with gear and buffs without a problem regardless of your starting stats.
Stamina is the best second stat all day if not taking resists into account.
If you are in a normal exp group you want Haste > ATK/STR > HP > STA > Resists and whatever else. Dex only if you have good proc weapons.
When raiding, you want Haste > Resists > STR/ATK > HP > whatever else.
You always want whatever provides maximum dps, but no amount of dps (str) or health can trump resists when raiding or in pvp. How high your dps is means nothing when you're dead.
Its safe to pretty much pump whatever stat you want on a rogue, by end game kunark or velious, a single item provides more stats than all your initial training points.
After str, sta is always important, while Agi means very little, dex is great for proc weapons, but in most situations proccing can cause you and your raid trouble if evade fails.