Get that HDMI cable for yourself good sir, if there's a local Five Below near your joint, you can get one there for five bucks. --- PR Advisor and Co-Founder for United For Tales: http://www.unitedfortales.org/
If it came with Red / White / Yellow cables, then yes, toss them immediately and get an HDMI cable. It will be a much better picture. If you have Red / Green / Blue cables and are currently outputting in 720p or higher then HDMI won't help much. Usually you can hit display or info or something on your tv remote to see what resolution your currently outputting. If its 480i then that's SD and you can definitely do better with HDMI.
Yeah I second the above poster. Dont pay a lot for an HDMI cable. Digital signals either work or they don't. There isn't really any difference in quality so long as the cable isnt physically defective.
Personally, I prefer to use the HDMI over the HD component cables that came with the xbox simply because there's less cords behind my tv. --- Currently Playing: Black Ops, Red Dead Redemption, Fallout: New Vegas