RaWr! I can't post! @.@ Will edit in my twice-deleted long and informative post with my thoughts on the subject as soon as this blasted hunk of junk allows me.
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Right, then.
In this particular case, here's what you should do:
At ninth level, take Weapon Spec - that damage'll help.
At tenth, take Whirlwind, the final prerequisite for WM.
At eleventh, take your first WM level.
At twelfth, put your ability point into STR.
After that, put all your ability points into DEX, and keep taking ranks in Tumble the whole while.
With items, you'll be better off getting DEX boosts. Keep a shield on-hand when you need AC, and don't be fooled into thinking that Max Dex applies to Attack Bonus! It doesn't!
(Well, unless Bioware's changed it since I last checked it, and I can't check right now. It -shouldn't- apply to attack bonus, according to canon rules.) So, keep some Full Plate in your pack until your Dex gets better than +8. (Remember, Max Dex applies to AC, so AC of 8 and 1 Max Dex is a total AC of 9 for the item. Only Full Plate and Padded Armor have 9 total AC, disregarding bonuses.)
Dual-wield. You've got the feats, use 'em! Get Improved Two-Weapon at your first opportunity in WM levels. You'll take a -4 to your attacks, but don't worry - one click, and you can swap your off-hand weapon for a shield, giving you a good bonus to AC (which you'll need) and to your AB. For your off-hand weapon, I'd advise a Swashbuckler's Sabre, as that one point of Deflection AC is nice, as permanent effects go. And you won't be sacrificing terribly much in terms of attack or damage power, as you're only getting two attacks with the offhand, anyhow. Don't forget, however, that Deflection AC does not stack.
Right, then.
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In terms of Duelist/WM... That could be a very powerful build indeed, in terms of damage, but would, as has been mentioned before, be weak in its defensive power. Expertise'll be handy... But I'll get to that in a moment.
In terms of RP, this build of Fighter/Duelist/WM follows an obvious course: learning from different masters, he slowly builds his own unique and powerful style of combat from the different disciplines.
In terms of mechanics... The build's weaknesses will be two: First, he will be weak as a mewling kitten in his low and mid levels, needing a long time to really bring everything (the higher-level benefits of the Prestige Classes) together. Second, his AC will be rather low. There will, of course, be the low Will Save, but that's a given. Fort and Ref won't be bad.
The real strengths? Well. There's really just the one: Damage. Attack Bonus will be on-par with most fighters around his level, but damage is where he really shines.
At Ftr 5/Dul 7/WM 7 (That's level ninteen!), and assuming a STR of just 12, he'll do the following with a copper rapier: 1d6 base, +1 STR, +2 Spec, +2d6 Precise Strike. 3 base crit (18-20), +3 Imp Crit, +2 Ki Crit, and Increased Modifier. All of that adds together to give 3d6+3 12-20/x3. Modal damage will be 13-14, with crits taking that to 31-32 at LEAST 16% of the time, assuming you're rolling against something a non-crit couldn't hit.
Give the fellow an addy rapier with a fire IV, some STR/DEX gear, and a good AB... Destructive.
I'll be laying out a full level planner for this late-level damage monster, with projected AB and Damage as well, on my lunch break. Why? Kicks and giggles, folks. Kicks and giggles.
In reality, this build would be incredibly frustrating to play - designed as a fronter, he'd have a piteous AC, so would be soaking up most of the party's healing, and only really doing damage on-par with one of the typical STR-monsters. When he got to high-high levels, and got fully buffed, he'd probably do most of the damage for the party, but... *Shrug.* I would not recommend trying to play a character who follows this idea - it just ain't worth it, and the RP isn't interesting enough out of the box to really shine. Then again, it's average characters who develop to be the most interesting, and the interesting ones that one has a hard time getting into and sticking with...
*Shrug.* As a thought experiment, though, interesting enough.
