rolandx: The model number (and dash-iteration) is found on the yoke/crane, when you open up the cylinder. Likely you got a 642-1 from the S&W run of 3,000 to 4,000 no-locks back in July/August 2008. (I'm surprised there any left unsold, btw.)
Also, CT grips are a good training aid to practice dry-firing, if you just can't wait to buy 'em and put 'em on (I couldn't either, I've been a supporter of CT products for over ten years). You can dry-fire at static targets (check to ensure 642 is not loaded with live round .... and then check again), and the laser is one sure way to analyze your 'trigger-wobble-zone'. instant feedback to improve/adjust trigger technique/control.
MAKE SURE YOU CHECK AND DOUBLE CHECKTO ENSURE THERE ARE NO LIVE ROUNDS IN THE GUN BEFORE DRY-FIRING!
Lagniappe: You've gotten great advice here from the senior club thread guys. I'll add a few suggestions .... start with non-+P ammo (.38 spl), when at the range, 130 grain fmjs (Remington UMC, Magtech or similar) and 148 grain wadcutters are good and soft-recoiling, too. You have CT grips, hopefully the 305's or 405's, which cover the 'backstrap' of the 642 (the exposed metal contacting your palm vertically, between thumb and forefinger). This is where the felt recoil stings people.
Practice dry-firing as much as possible (buy some snap caps, e.g., Pachmayr A-zoom, anodized aluminum colored red to distinguish from live ammo), watching tv, after a workout, before bed, upon waking, whenever. Practice strong and weak-hand.
MAKE SURE YOU CHECK AND DOUBLE CHECKTO ENSURE NO LIVE ROUNDS ARE IN THE GUN BEFORE DRY-FIRING!
This will make your trigger pull consistent and will strengthen your hands/trigger finger. Wouldn't hurt to get a physical rehab-'squeeze' ball, or getting a set of small 2 1/2-5 lb. dumbells (just need to hold the dumbells at your side, do 'shoulder shrugs', roll them in your hand, etc.,), b/c the gripping is the important thing to develop hand strength both to better control the gun and to better absorb recoil. You can exercise your hands, when not dry-firing. It is key that you try to continuing increasing the ability of your muscles to do work - by 'triggering' them or stimulating them - so that when 'performance' is required (whether at the range or, God forbid, in a self-defense situation) your muscles have both the capacity and memory to do it.
When you get to the range to practice, you don't need to shoot all the ammo at once. Work your way up incrementally, from 5-10 rounds, at first. Then spend time dry-firing at home between sessions. It will be more economical, you will notice faster improvement, and you will have less risk of fatigue/shock injury to your hands. If you shoot too many rounds in one session (particularly the first range session) you may get injured, setting you back weeks or months.
For example, 5-10 rounds your first range trip on Monday, target at 3 yards. Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday: 100 dry-fire pulls (sets of 10-20 at a time) EACH DAY. The following Monday, 10-15 rounds. T,W,Th,F,S,Sun: 100-150 dry-fire pulls (sets of 10-20 at a time) EACH DAY. The following Monday, again, 15-20 rounds, target at 5 yards. Incrementality is key, work your way up, build strength and recoil tolerance, over time.
MAKE SURE TO CHECK AND DOUBLE CHECK TO ENSURE THERE ARE NO LIVE ROUNDS IN THE GUN BEFORE DRY-FIRING!
Be safe and good luck! (And there's plenty more info. in this amazingly long instructive club thread, if and when you have the time.)