It takes a bit of research I'm afriad. I thought this was the way to go as all my friends were doing it and were on a simialr wage and they were only just managing. I signed up with the Nottinghill Housing Trust and also registered with estate agents and found that the repayments on a full mortgage compared to the part-rent part-buy weren't always so different.
One of my friends is now kicking herself for not looking into it properly because I bought my property in full on a mortgage and repay �800 a month.....she has bought 25% of hers and rents 75% and her repayments are �750 per month - both are 2 bed flats. When she sells, she'll onyl get 25% of the sale price, where-as I'll get 100%.
So my advice is check it all out - it sounds like it should make things much more manageable but it's not always the case.