Can I stream content from my iMac to my TV?

I'm truly a novice when it comes to this, so please forgive if this question belongs in the wireless section.

We live on a farm and have analog (10+ years) TVs and just finally got DSL in our area 🙂

I have an iMac (Intel) that is located in the upstairs office (the only room with the DSL connection.) I would like to see if we could have the internet content appear on our TVs (whether the main one downstairs or the one in the bedroom.) I am confused about whether we need a wrieless router or if the iMac actually already has that ability built in (isn't that what Airport is?)

If so, do I just need another computer, laptop or hard drive or whatever with Airport downstairs by the TV to be able to connect to the TV and stream the content by turning on Airport?

Or do I need something else?

I realize we will likely have to get a new TV or monitor. We don't have things like Wii etc., which I gather can also be used for this purpose.

Do we need to get an Airport Extreme box? or a wireless router? There are no Mac people within hundreds of miles of us and everyone (including the phone company) are all PC people.

Many thanks!