Running along a beach for 1 or 2 hrs is not gonna help paintballing what-so-ever!!!
Paintballing is all about short bursts of speed...slight stamina, but games rarely go over 5 mins really and dont include long periods of running.
Try spriting training, doing shuttle runs or similar. What Rosie mentioned earlier bout sprinting/jogging alternatley is good.
One me n mates tried...not really recomended, but i guess it would work...is put a tread mill on a couple of km/h slower than you're full out sprint...stand leg either side of the belt as it moves, then jump on (running immediatley!!!) for 20 secs, then jump off...
as you can tell, this could easily result in painful injury!!! but is all good if you do it properly...(may give your local gym staff a fit thou!!!
)