Help with newbie lens

Hi,

I've descided to buy the 450D as my first SLR, which comes with either of

• 18-55 IS

• 17-85 IS USM

(the two kits provided by my local store)

I wish to have great pictures of:

• my kids running around indoors

• my kids running around outdoors

• landscapes (during holidays)

• portraits

Our lighting at home is not that good, so I'm thinking that buying a SpeedLight 270EX along the road might be a good idea. This would elimate the need for a low F-value on the lens, right?

I understand the the USM has faster autofocus engine, which would be better than non-USM when taking pictures of moving kids, right?

For portraits I'm thinking of complementing with a 50/F1.8 lens, to achieve the "blurred backgrounds" (unless I find that the kit lens I descide on can do it well!).

I understand that IS will be of no use to me with moving objects, right?

The reason I'm moving from my G7 is that it's simply not fast enough to follow my kids' movements!

Thanks for any help!

Martin