Well firstly, 100% mortgages are now almost 100% impossible to find - thanks to the Credit Crunch. As for your credit ratings, you will be financially associated if you get a joint mortgage. Have you thought about only having your partner on the mortgage with his parents or a guarantee as this will be fine in him securing some money, and then you can go on it with him in a couple of years time. This is because bad credit stays on your record for about 6 years, and so it would be best if you can wait.
Also, have you looked into first time buyer schemes? What do you both do for work? You may be eligible for Primary Worker mortgages, or even better still, the government have just launched a scheme called My Choice Home Buy. There is lot's of help for first time buyers!
If you're not a first time buyer, given the current opinion on new mortgage customers and given your ratings, I would probably rent for a couple of years, try to save as much as possible, and then, when your credit has improved and you have a deposit, the credit crunch would have passed, house prices may have dropped a little, and you'll be in for a much better deal.
Best idea would be to consult an independant financial advisor - some are free (and the free ones are normally the best!)