I found this video on youtube on how to flash Velocity:
Is that tutorial good? Will it brick my phone? Should I look for a different tutorial?
this is what i think you should do, go back to this post
http://androidforums.com/lg-ally/358014-how-make-my-ally-less-laggy.html#post2842645 (Post 5) read the "To Root With SOC or not. . " thread. then consider using the 2.2 root guide i linked to there also. the root guide downgrade to 2.1 ZV6 and gives you fastboot access. then flashes stock rooted or velocity via fastboot. if you choose velocity you will need to DL the 1.1 zip. you may need to use LGNPST to downgrade.
now if that's too much. well then i hope you're never in a pickle and need fastboot. but DONT DONT DONT use that guide and dont use Clockworkmod Recovery, you can do it like Cl8rs said,
http://androidforums.com/lg-ally/358014-how-make-my-ally-less-laggy.html#post2843364 (Post 9) or use dots link and flash the recovery manually (this will work better than ROM manager)
http://androidforums.com/getitnowmarketing/330813-all-one-recovery-thread.html
All the info you need to get Velocity up and running is right here. i dont know why youy are looking for something EASIER, if you need someone to walk you through it because you cant do some reading of your own or this is all too complicated for you, then consider NOT rooting it. and again you NEED to do research before doing something like rooting your phone. unless you have money to blow if you make yourself a shiny paper weight. at some point something WILL go wrong. big or small its gonna happen and YOU need to know about your options to fix it and not just rely on the people here. be self sufficient. im in no way talking down about getting help here, some of these folks have saved my ass. im just sayin DO YOUR OWN RESEARCH. well enough of this. i have a feeling this will fall on deaf ears.
and for going back to stock, once you root your warranty will always be gone. whether verizon knows that or not is a different story. my vibrator went out so i went stock and got a replacement, they actually spent a good while trying to prove it was rooted before issuing a replacement.
BUT you can bootloop it, get stuck without recovery and in that case you only have 3 options, (2 if you dont have fastboot) 1. take it to verizon and play stupid (wont work if you flashed a ALT splash or the Splash screens that come with velocity) 2. FASTBOOT

3. LGNPST