Very Weak Wifi signal- core duo OS 10.5

Please help!

Seen many threads on this issue but all are not the same problem...some are non-problems, some are not, this one is definitely a real problem suffered by many. If you suffer this problem you, like I, feel that your macbook pro begins to resemble a rather expensive paper weight as the wireless wifi capability is basically nonexistent.

The problem:
Dismal wifi signal strength

Symptoms and all clues that come to mind:
My macbook pro hovers on one bar and bounces to 2 on occasion and web is "phone line" slow with basically unusable upload and download speeds.

My girlfreind's machine (mbp w/core 2 duo 2.33) in the very same spot shows full signal indicator and web is snappy...upload and download speeds are a 5-100 times faster than mine.

This has not always been the case...in the past both machines performed identically.

Both machines have had HD's replaced recently.

What can be causing this and how can it be fixed?

Is it a software/firmware thing? A network setting? Is it a matter of the case being opened and the "bunny ears" adjusted and tin foil fitted to em? If I cannot actually fix it, is there some sort of signal booster I can get (cannot move signal source)?

Hate to say it, but I am better off with a crappy PC that I can actually use at this point than my impotent mbp.

Please do not post if you think I should move my router or that the MBP just does not effectively receive wifi due to it being made of aluminum.

Thanks in advance for your collective expertise...