upgrade to n for smoother netflix etc streaming? How?

I have been running a Linksys 54G for several years. I have my
desktop wired to the router and my laptop (old Thinkpad with antenna
in the back of the screen), picks up the signal all over my house,
usually at 54.

However, I can't quite stream a Netflix film on my old Thinkpad
although its antenna also runs at a maximum of G. Picture begins to
break up and sometimes it stops altogether while it seems to try to
buffer.

I got a Cisco Linksys E4200 n/dual band and the PCMCIA card to go with
it. Both support wireless n and both are dual band.

Many hours of tech support confirmed that my portable, the PCMCIA n/
dual band card, could not see the router. Or, when it did, it ran at
speeds of 18 or 40 rather an the 300 it's supposed to achieve.
Occasionally it got to 100 but quickly began to drop even when I was
within 10 feet of the router.

Linkssys had me adjust router settings and eventually had me flash the
router even though the revision was technically the same.

Result was that the E4200 stopped working even wired to my desktop and
of course, the notebook card never functioned with any kind of
regularity although the internal antenna works fine up to G. I
returned both and reinstalled my Linksys 54G router.

Is there a way to upgrade both the router and the notebook (Thinkpad
X40) to wireless n and would that produce smoother streaming? BTW,
memory on my Thinkpad is full and I don't think that's the problem.

Is there a combination that would work?

Thanks for reading this long explanation and for any suggestions you
can offer.

Louise