Spuk87, I agree with Spearmint-R33 that you'll need to spend your 5 weeks wisely.
I'm also getting fit for selection at OASC and about 6 weeks ago I did a bleep test and got 9.8, which is pathetic. I then started interval training.
I warm up for around 4-5 mins with a gentle jog, sprint for 30 secs and then jog for 60 secs, repeat this 12 times, then cool down for 4-5 mins. It should take around 30 mins including warm-up and cool-down and when done properly you should berely be able to walk by the end of it.
I've been doing this for about a month, 2-3 times a week, and have seen a dramatic increase in my fitness. Doing this has cut my 3 mile time down by 1.5 mins to 20.40 and my 1.5 mile by about a min to 10.07, these times definitely weren't possible 6 weeks ago.
This is very similar to Spearmint's advice to find a hill to run to and then run up 10x. I just thought I'd reinforce how good this training is. It will increase your speed over a short distance which is good for OASC because as far as I'm aware long distance runs aren't done there. Another benefit is that it's a lot more interesting then just running at the same pace which usually means that you'll stick at it.
If you want any more info on this and have got a spare half hour then just google interval training, there are loads of good websites.
Best of luck
