Nazggul

Comparing swimming to running and biking, I'd have to say that it is easiest to get your heart rate up from running, biking, then swimming, in that order. Sweating has little to do with serious weight loss, that is only water weight that you will (and should) put right back on once you rehydrate yourself. And, by the way, you do sweat when you swim.

If you do choose swimming as your preferred exercise to lose weight I would work your way up to using zoomers and paddles or swim gloves. Contrary to what you may think, these tools will increase resistance during the swim and actually make you work harder while maintaining good form. Also, try to get into a masters program. Nothing is better for motivation that swimming with groups and having a screaming raving lunatic coach shouting at you from pool side to move yer arse. ;-)


EDIT:
I thought I would throw in a basic interval workout for you to try. I still do this one once in a while. Distances are in meters. Typically you are swimming in a 20 or 25 meter pool, if you're lucky you have access to an Olympic sized pool, 50 meters:

Warm up:
200 Free
200 Back (losens the shoulders up both front and back)

Set #1
4 x 50 @ hard pace :40 (30 seconds rest between)
400 easy

Set #2
4 x 50 @ hard pace :40 (30 seconds rest between)
300 easy

Set #3
4 x 50 @ hard pace :40 (30 seconds rest between)
200 easy

Set #4
4 x 50 @ hard pace :40 (30 seconds rest between)
100 easy

Drills:
200 Kick
200 Pull


I usually sub the 50 meters for 100's, but to get closer to the HIIT type workout that others have mentioned you will probably want to stick with the 50.

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