The Tiger Moth with the 150mAh pack is quite uninspiring as far as duration. My suggestion is to replace the pack with a 7-cell, 300-370mAh pack of 2/3AAA NiMH cells. For the same weight, you get at least twice the duration, and the extra cell gives you more power. You can run at lower throttle settings, which will further extend your flight time. A friend of mine routinely gets 12-15 minutes on the NiMH pack.

If this is your first foray into electrics, it's probably a good idea to stay away from Lithium Polymer, LiPoly batteries until you have some experience charging and discharging batteries. A totally uninitiated novice with no electronic experience will tend to make mistakes the first few times they charge a battery. Someone new to flying, or whose skills are rusty will crash a lot. LiPolys do not tolerate many mistakes. You can destroy a very expensive battery, or burn your house down if you use the wrong charger, or settings, or if you crash the plane hard enough to damage the cells. You need to be extremely careful with LiPolys; make sure you have the right charger with the correct cell count, keep an eye on them while they're charging, and never put them in your car immediately after a crash.

That said, if you still want to forge ahead, make sure you understand the risks and rewards associated with this still-experimental technology. Having electronics experience is a major help. You'll also have some of the requisite knowledge if you're a glow pilot who is very conscientious about caring for the batteries in your planes.