Hmm. Depends on a lot of things. First up, just as a quick note, ANY computer that you're running will need a keyboard/trackpad of some type for certain things. That being said, I was rather surprised when my TV remote actually worked out of the box with my TV/HTPC combo.
My setup:
TV: Vizio 42" LED Razor
Computer: Raspberry Pi 2 running OpenELEC.
Keyboard: 2.4ghz mini keyboard/trackpad (one of those little $10.00 rechargeable units).
Apparently, the Pi 2 and the Vizio 42" both support HDMI-CEC, so if your TV that you're hooking it to also supports HDMI-CEC, and the computer supports it as well, then your regular remote, in TV mode, might possibly control it as well. That being said, the little $10.00 keyboard/trackpad does the job just fine as well.
BTW, if you haven't already built the computer, I'm REALLY going to suggest the Raspberry PI 2 for running OpenELEC. It's an amazingly good setup, and it's cheap. Just a quick note, get the Pi-2, NOT the regular Pi. The Pi-2 is a quad core ARM, much more powerful and capable, and draws a few watts at most, and is completely silent. A full setup, including keyboard?
R-Pi 2 kit: Includes case, power plug, Raspberry PI and SD card - $60.00
Keyboard: $10.00
OpenELEC: free.
This is the keyboard I have:
http://www.newegg.com/Product/Product.aspx?Item=9SIA6FY2F98033&cm_re=rii_mini-_-9SIA6FY2F98033-_-Product