After playing around, I tweaked my current frost build to this:

Arcane Talents (16 points)

# Improved Arcane Missiles - 5/5 points
Gives you a 100% chance to avoid interruption caused by damage while channeling Arcane Missiles.

# Arcane Subtlety - 1/3 point
Reduces the threat generated by your offensive arcane spells by 20%.

# Arcane Concentration - 4/5 points
Gives you a 8% chance of entering a Clearcasting state after any damage spell hits a target. The Clearcasting state reduces the mana cost of your next damage spell by 100%.

# Evocation - 1/1 point
While channeling this spell, your mana regeneration is active and increased by 1500%. Lasts 8 seconds.

# Improved Arcane Explosion - 5/5 points
Reduces the casting time of your Arcane Explosion by 1.5 seconds.

Frost Talents (35 points)

# Improved Frostbolt - 5/5 points
Reduces the casting time of your Frostbolt spell by 0.5 seconds.

# Ice Shards - 5/5 points
Increases the critical strike damage bonus of your Frost spells by 100%.

# Improved Frost Nova - 2/2 points
Reduces the cooldown of your Frost Nova spell by ?.

# Piercing Ice - 3/3 points
Increases the damage done by your frost spells by 6%.

# Cold Snap - 1/1 point
When activated, this spell finishes the cooldown on all of your cold spells.

# Arctic Reach - 2/2 points
Increases the range of your Frostbolt spell and the radius of your Frost Nova and Cone of Cold spells by 20%.

# Frost Channeling - 3/3 points
Reduces the mana cost of your frost spells by 15%.

# Shatter - 5/5 points
Increases the critical strike chance of your frost spells against frozen targets by 50%.

# Improved Cone of Cold - 2/3 points
Increases the damage dealt by your Cone of Cold spell by 25%.

# Ice Block - 1/1 point
You become encased in a block of ice, protecting you from all physical attacks and spells for 10 seconds, but during that time you cannot attack, move, or cast spells.

# Frostbite - 5/5 points
Gives your chill effects a 15% chance to freeze the target for 5 seconds.

# Ice Barrier - 1/1 point
Instantly shields you, absorbing 455 damage. Lasts 1 minute. While the shield holds, spells will not be interrupted.

Fire Talents (0 points)

# None

Now I have seen alot of builds, that either focus on Frost/Arc - Fire/Arc or all Fire/Frost. What I dont see alot of, is a Fire/Frost.

I am new to WoW, came from EQ2 - EQ - SWG - AO - DAOC, so i have played many MMO's and WoW is the most intreging simply because of the complexity of the characters in creation and the ability to PvP (got hooked on it with DAOC and AO).

Is a Fire/Frost build that gimping that no one uses it? Or is just not that viable?

I guess its because people want to specialise in either fire or frost.
If you are jack of all trades you are master of none;)

Havent tried a build like that, so wouldnt know for sure tho.

It seems that going Fire/Frost would cause you to lose a lot of useful tools from the Arcane line. I don't know if getting the spells from the other Fire/Frost line would outweigh what you lose in Arcane.