karaoke microphone for laptop

I love to sing, and use my headphone mic set for myspace karaoke. However, I've noticed when I try doing this with my laptop, there is way too much lag time between when I sing and hear myself through the head phones. does anyone know what could be causing this? I have checked settings and there is no echo set up. I am wondering if it could be caused by a short in headphones? and Also what is the best mic I can get for singing on computer for under 50.00 ? pleases get back to me soon, I bought this laptop for school and singing on it and now i can't sing on it HELP!!!!Thank you so much!