Dell Vostro Wireless Problem

Hi guys my girlfriend has give me her dell vostro 1700
since she has bought a new laptop but her dads friend installed windows 7 and has deleted the recovery parition so which is a downfall because i really needed that, so i installed windows 7 since thats the only disk i got fresh onto the computer but i dont think this laptop is compatible etc.. anyhow i have all the correct drivers since i used driver easy but connecting to the internet is fine but its slow and then fast it fails to download files which are big- its not the internet since i have 2 other laptops which work fine (not turned on same time) so shouldnt be problems but its just so slow - so i have used a wireless usb connector which connects to my router and it seems to be working just fine with that but i dont really fancy having the usb device plugged in all the time but i notice the computer kinda lags also so im not sure if that will have any conflict with the internet speed. anyhow its just annoying me now since i aint got no recovery parition to put it back to xp so does any 1 have any suggestions on what i could do or check which may be making the internet slow?