Subdomain or new domain?

how much does a subdomain affect serps?

[chasing something]

i am building a new site that relates- in broad terms -to an older site. it could fit in with the older site and i'm considering just tacking it on as a subdomain, but i'm wondering how much it will affect serps, not to mention the sandbox on the flip side of the question.

if it's seo'd well and i do a link campaign specifically for that subdomain, can it do as well in the serps as buying a new domain, or do SEs prefer domains? it is a highly competitive niche.
should i use it as new content on the older site, or would it rank better seperately?

i can't decide and want some opinions:) sandbox or subdomain?

[troels nybo nielsen]

I think I would:

1. Acquire a new domain and build a small website with relevant text on it.

2. Build the new website about your secondary topic on a subdomain of the old website.

3. Link to the new domain somewhere on the old website so that search engines find it.

4. Watch how search engines treat the new domain.

5. When the new domain begins to show in all relevant search engines I would move the website to it from the subdomain and of course make redirects.

[chasing something]

i like that idea, thanks:)