"install" wordpress theme on wordpress.com

I have a blog hosted on [login to view URL] and a wordpress theme that I'd like to use on it. Unfortunately, [login to view URL] does not allow to upload custom themes. What it does allow is to use custom CSS. What I'd like you to do is to choose a suitable theme from those offered by [login to view URL] and then change its CSS so that it looks like the theme I have to the extent possible. So, I'd like to continue to host the blog on [login to view URL] but make it look like the theme I have. Please ask me about the details in PM. Also please mention in PM what experience do you have with wordpress. The task is urgent, please bid appropriately. Thanks.