Internet is not working properly…

Since few days my internet connection is not working properly, it is performing very very slow…even disconnects frequently…Details of internet connection & Desktop/software are as below…

Internet : USB modem (shows full range with 230 kbps speed)

RAM : 2 GB

Processor : Intel core 2 Duo

OS : Windows XP

IE : 6.0

Space available on C drive : 500MB

What could be the reason & how to solve the problem? Please help…