custom 404 & search engines

[kaibobble]

Does anyone know how search engines deal with custom 404 error pages.

so for example if you set a site map as your 404 page would search engines such as google carry on following links or would it recognise it's a 404 and stop or rank you lower in the search engines for it?

[AdamGundry]

Please try to avoid posting the same question in multiple places. This is being discussed here.

Adam