802.11b is 11 meagerbits (typo intentional) and the old router's CPU can limit that to even less. So there's choices to be made here.
I have a brand new t61p model # 6459. It has 4 gb ram 2.5ghz processor and I have windows xp pro which i downgraded from vista too. I have a intel wifi link 4965 agn. My router is a linksys 2.4ghz 802.11b. I know that this is outdated but, i have 3 other computers. 2 Pc's one wireless and the other hardwire. i also have one other old dell laptop with a wireless card that only supports 802.11b. I go to speakeasy.net and i have ran the speed test on all 4 computers( i have used a couple of other sites for verifiaction). The average for the 3 computers(not the t61p) is 2800kpbs. I should supposbly have 3000kbps according to verizion but that doesnt matter. Anyways when I run the lenovo on the speakeasy website the highest download rate i got was 1000kbps. Genreally its around 700kbps. I have made sure all computers have Excellent signal 100%. I noticed the laptop was slow using the internet on downloads and even web browsing and its a fairly big difference from the others. I feel like something is restricting my t61p. I have plugged in the usb drive that one of my pc's uses which got the results 2800kbps, when i plugged it into the lenovo i got around the same results. I also have plugged an ethernet cable into the laptop and I then was able to get 2800kbps. Please please please help me! If you need anymore info i will get it.