Internet connection problems wireless vista premium

I have a new Dell Inspiron 531 with Vista home premium and have had many problems with connecting to the internet with a wireless connection. The dell computer has a built in wireless card. The router I am using is a Linksys WRTSL54GS. I am using wpa personal encryption. For antivirus I am using the Mcafee AV that came with the computer. Heres the problem. Sometimes it connects and when it does its usually very slow. Many times actually most times I cannot connect to the internet. It shows a connection to my router and says limited connection and or sometimes it gets stuck in the identifying the network. I have called Dell support 3 or 4 times on this and they have been worthless! They tell me to remove parts of Mcafee and it seems to work and it does for a bit but it is slowwwww. I told support that it was slow and they tell me its my ISP thats slow. Thats not true! I have roadrunner cable and I have a dell notebook also using the wireless connection and its speedy as it has ever been. Its just the new Dell desktop that is slow or doesn't connect. Now I forgot to say this. If I boot into safe mode the wireless works great and the internet is fast. So something is happening when I get a full boot of the system. I think its probably related to Mcafee and Vista problems. Suggestions? Please help I am tired of talking to someone in India who cannot speak properly Ray