<< Specifically, the TX, FX, and VX chipsets automatically disable the L2 cache if more than 64MB of RAM are present. >>
That's not true. The L2 cache is not disabled, it's just that RAM addresses above 64MB are not cached in the fast static RAM of the cache, but rather in the slower system RAM. So on those chipsets you will see a performance hit of maybe 2-3% if you have over 64MB of RAM.
Since it's a laptop, you maybe don't have a TX, FX, VX, or HX chipset. You might have the MX mobile chipset, not sure about the cacheable limit for that one, although I have seen laptops with that chipset ship from IBM with up to 104MB of RAM.