Echo the shoes advice - it's worth going to a specialist shop, getting something which really suits your feet, then after that get the 'last years' models off the Net.
If your knee is still giving you grief tomorrow, try getting some ibuprofen gel. I agree with Jan, you're unlikely to have got a case of 'Runner's knee' that quickly (very accurate description though Jan, and something I know far more about than I'd like )
So, what Race(s) For Life are we signed up for ? I'm doing Brighton & Newbury (bang goes my anonominity ! sp ?) I'm running Brighton then going back to meet up with my mum & dd (4) who are doing their first, then the following week am doing one with my Rosemary Conley class.
I know every year I promise to shut up about it but never do, we must surely be able to get a Mumsnet Race For Life team together this year ? Or is this where the 'meet-up' threads suddenly go quiet ?
BUT, all you diet thread peeps, note that a 10 stone person who runs a mile in 10 mins will burn 100 calories, so RFL = more than a Mars bar or 1/2 bottle of wine plus the boosted metabolic rate continues burning the calories after you've stopped !