As far as I know, changing hosting company will not affect your SEO ranking.

No, it will affect, changing hosting mean changing the IP address of the website, if it is not done right, it can ruin your website SERP

changing host name really effects the page rankig

I don't think your ranking in serps will be greatly affected by changing the host. As long as everything is done the way it should be done and there is no extended downtime, the changes encountered should be minor.
Ranking in serps, according to Google, is determined by around 200 factors (the most important ones are probably the content, keywords and inbound links). As long as these don't change and as long as the search bots can crawl your site, it doesn't really matter who are you hosting with.
You only problem by changing the host will be if you used Yahoo's stuff (forms and whatnot), you might have to rebuild/modify your website.

PS: So, OP, did the host change happen? Have you seen any changes in ranking for your keywords in the result pages?

You may see some effects initially but you should bounce back in the SERPs quick.

The only way is to try it, there's so many rumours flying around about this!

So let us know how you get on please

changing hosting company will not effect on your keyword ranking