I don't think z4root works anymore since the 2.2.1 update. Otherwise I believe it should work with no extra work (as it did for me before I did the update). However, that's with my Sprint Intercept so I am not sure if z4root ever worked on Virgin Mobile phones. Check the other posts though regarding the super one click way to root. Worked perfectly for me (after it finally made it thru all the steps).
HOW!?!?