Um, I assume you have at least a 512KB connection, 'cus you'll get nowhere with less than that.
For ease of setup/use, I recommend
OmniSecure which is just a simple install and off you go.
It's not as configurable as Apache, but you don't need all that for just a regular website.
You'll probably also need a static IP address, so if you don't have one then get one from no-ip.org or dyndns.org or somewhere.
Oh, and you'll want to make sure you have a decent firewall in place, because you'd be a bigger target for hackers than a regular machine.
Um, strain-wise, your CPU, RAM and HDD are the only bits that should be affected, but unless you have complex server-side scripting and/or a lot of visits, you'll probably not notice any difference.
I think that covers everything, but others here can probably fill any gaps if I've left any, and obviously ask if you have questions.