The signal is not stable only. You can compensate it with a good router.

Just bought a Dlink Extreme N router. I can say definately worth it if you are fed up with slow transfer speed. I used to get crappy 100kB/s transfer rate most of the time. Very seldom can reach 1MB/s. Was using DIR 300. After upgrading, transferring from my pc (with Linksys USB Wireless G) to my bro pc on LAN cable, speed was steadily 2MB/s+ whereas it was not possible to reach even 1MB/s. The most noticeable one was from my pc to my laptop with Wireless N card. Used to be around 100kB/s ++ but now 700-800kB/s. I tried to disturb it by trying to connect from my wife N85 and still it can send 600++ kB/s. Not bad...

I appreciated on your all inputs;

However, this is definitely not the ROUTER or BRAND issue; The actual problem is the USB WiFi adaptor overheat after 24*7 continuous running, because my desktop is running all day & night as download server.

I solved my problem by replacing with the WiFi Draft N PCI Card, I running non-stop more than 2 weeks without any issue.

What (model) card is that?

Hehe...
My computer also run 24/7. So whether its adapter or router, I know better.
If you think its not range problem, then why you upgrade to Wifi-N?
Wifi N has better range, be it adapter or router.

When I was still using DIR300 (G router), I could get better transfer rate on my laptop than my desktop due to the built in N adapter compared to my Linksys G adapter. So the limit is the technology and not the brands. Why dont you use back your old card and borrow someone N router to do a test. You can get way better transfer rate using N router with G adapter compared to G router with N adapter. If you bought a N router, you can benefit a wider range of usage. The reason I recommend a N router is because it can do MIMO. Thats allow you to benefit the transfer from two devices which are using wireless connection at the same time. As a matter of fact, the transfer rate from my laptop to my desktop is 6times faster when using N router compared to when using G router.

G adapter -> G router -> N adapter = 100++ kB/s
G adapter -> N router -> N adapter = 800++ kB/s