Hi,
Have you tried to set the latency higher ? Which driver do you use (ASIO, WDM, MME.. try switching them). If you don't have ASIO, look for a driver called ASIO for all.. (you need to search this for more info - I've not use it, but it works for some here). These alone may solve audio playback issue.
Also check if your notebook processor meets the requirement :
http://www.cakewalk.com/products/SONAR/X2-Producer/ (bottom page)
Unless you also wanted to do recording.. in that case, keep reading..
Although the term sound card also applies to DAW usage, look for one that is classified under audio interface. A good starting place :
http://www.sweetwater.com/shop/computer-audio/audio_interfaces/ Almost all items listed that is good to your budget can be used (except the USB 1.1 interfaces and you want to avoid using this, as it gives you only 2 channels max).
Select the USB 2 interfaces for best compatibility :
http://www.sweetwater.com/c695--USB_Audio_Interfaces You need to decide how many inputs / outputs you required / with or without MIDI.
Commonly suggested brands : Focusrite, Roland (more to come from others :)..
Select an item or two and come back for discussion. Search for older info with many good advice as this topic pops up from time to time.