Amusingly, even if you have your very own TLD, it doesn't help you. Most browsers send single-word lookups to a search engine before they send them to DNS. Try "ca" in a browser. There is a web site at "ca". But to get there, you'll have to use "ca.", to force a DNS lookup from the root. Nobody knows to do that unless they're into how DNS works. There are some low-level bugs embedded in very common C libraries which cause problems with single-word domains, and they probably won't be fixed.
As for the original poster's advice, the price of the domain you want in .com is probably more than YCombinator's initial funding. With all of today's domain hoarding, the ".com" domain usually comes later. Facebook started as "thefacebook.com".