Join a Versus match and wait until you become the Charger. Make your way to an open area, run up behind the survivors and hit the to charge. If you have enough room you should carry off a survivor without any issues.
System Link Techniques
Almost all Versus achievements can be earned in private games or via System Link. Wait until you spawn as the various Special Infected and use their primary attacks on the survivors.
You will need two controllers and possibly two players. Whoever is earning the achievements will be playing as the Infected the first time around, then swap over when you have done whichever achievements you require.
Use the methods supplied under each achievement and you should have all the Versus achievements in no time.