How to convert 404 error code in 301 permanent redirect

[relyt]

I want to convert my 404 status code in to 301. I have top indexed site in SEO and I don't want to loos my position if bot don't found my page.For some URLs I am getting 404 status and by redirecting to some another page with 404 status code is not good thing for SEO.So I want to convert status code to 301 so it wont affect my indexing.I want to set 301 status code when it gives 404. My site is in asp.net 1.1 and I have tried lot of solution before.Some solutions are giving me 301 instead of 404 status code but they gives in second step. Means first they are giving 302 then they are giving 301. But I don't want to do that. I want directly from 404 to 301.Is it possible with asp.net 1.1 and IIS?Please help me in this.Thanks