boosting a car battery

I have a 2007 BMW 328i 6-speed manual. The battery is the original one (I assume) and it's getting bad. If I leave the lights on for more than a few minutes, it dies, if I don't drive it for a day or two, it dies. I always get it jumped either by jump-starting it on a hill (I always park on hills now) or I have gotten a boost from the van once before.

The annoying part about my car is the battery is in the trunk, yet you can't boost it from the trunk you have to boost it through the terminals under the hood. The 2nd annoying part is I can't go to Walmart and get a battery and install it myself, I have to get a BMW battery from BMW and have BMW code it to my car in order for it to work correctly.

I've heard from people that when a battery gets bad and you have to start boosting it it will only make it worse. I don't have the time to take it to BMW but I don't want it to get to the point where I go to get gas, shut the car off and it dies.

Today I was parked at school on a hill and I put my key in, hit the clutch and brake and when I hit STOP/START it was dead. I don't think I left anything on but I couldn't tell since it was so dead.

2 questions:

- Is jump-starting a manual car by putting it in first gear and popping the clutch while it's rolling bad for the car mechanically?

- Is jump-starting a car using jumper-cables bad for the other vehicles battery?