One thing you can do is to install a traffic tracking tool so you can see on the reports where your site was found and what keywords are used in the searches to see your site..
google webmaster tool does have that feature. But I don't think you can specifically select keyword you want.
U can use google webmaster tool for this..google webmaster have feature for this but this doesn't show the exect position.
I mostly use IBP, it a great tool , but is not free, it works great and you can specify the search engine and country you're interested in.
IBP, scrubtheweb and submitexpress is good tools. But I recommended google webmaster tool for website. It is easy to use and total free for use.
If you are using firefox, then you can install the add on "rankchecker"from seobook.com. This is a very handy tool and can give you ranking details for Google, Yahoo and MSN(Bing). You can also check country wise ranking for your targeted keywords.
You can have the option to use the google analytics tool which I think is the best as well as awstats which usually comes with cpanel, etc. Histats is also a good program!
Use IBP software its a best software for tracking all info about you SEO of your site.They can also show your site ranking on search engine with specific keyword.
Google Web master tool is always better. Because that shows the position for key words, But you cant chk it for your requiered key word.