As someone in a similar situation, (I've had TM for 8 months now) I too have tried to create a vertical beam weapon. While I haven't achieved a true beam, I have been able to simulate the effect using a smoke trail. Here's how I did it:

(1) Make a projectile (or borrow one from, say, the "atom bomb mod") and change/add these lines.

(2) SmokeTrailEnt = SDI laser
smoketrail = 1
iterations = 20
(I used 20 iterations in my mod. but use a higher value to make the beam more solid and less puffy.)

timetolive = 6

HitScan = 1
HitScanRange = 200.0
(And now for the guidance...Some like very guided weapons, some hate them. I fall in the middle. Alter values, esp. the guide values to suit your taste.)

spiral = 10.0
spiralramp = 0.01
spiralperiod = 0.9

guideramp = 1.0
guidebias = 2.0
guidespeed = 2
guidemax = 2

Gravity = .4
(Increase this value to lessen the time between launch and strike times, but IMHO the psychological effect of waiting to die is as powerful as the impact of the strike itself.)

LaunchInertia = 0.5

Detonate = 1

Transitory = 0

(3) Create or borrow a smoke ent named SDI laser with these specs.

Class = smoke
Type = SDI laser
Texture = sprites/LaserBall.bmp
(N.B. Choose or make a sprite that fits your need.)
SizeBias = -2
Width = 2.0
Height = 2.0
Base = 1
(I like a relatively small beam profile)

grow = 1

blend = add

fade = 1.0

fadebias = 0.5

timetolive = 3
(I like my beams to fade slowly, reduce this value for a quicker strike value.)
randomrotate = 1

(4) Make sure you have a cool exploent and explohitent values in your projectile file. I ajusted the specs for the explo ENT, "lobberhit" from the "Rusty Bomb lobber" created (I think) by JVortex.

(5) Add a cool sound...

Although this post is very disorganized, I hope it gives you some idea. If you want to see my ENT files, drop me a line, I have several new weapons and tank mods (some completely new) I've been dying to share.

--LB

I'll clean them up and do just that.