I dont really get what you mean
"32bit O/S = 3.25GB MAX
64bit O/S = 128GB MAX"
RAM limitations based on 32-bit (i386) and 64-bit technologies. The way a 32-bit system is laid out, you can have a total of 4 Gigs *total* system usage. Now, keep in mind that your chipsets, PCI slots, AGP/PCIe slots, etc. all count towards the total 4 Gigs. After all the needs of the system are satisfied, the computer then tells the RAM controller that it can use whatever is left.
If you have 1, 2, or 3, Gigs of RAM, it's not a problem because you won't use more than 1 Gig to run all the other resources the system needs. However, if you have 4 Gigs of RAM, the RAM controller will only recognize around 3.25-ish of it, since the system already took the resources it needed to run the above-mentioned items.
64-bit uses slightly different technology, so the 4-gig barrier is not an issue. As far as the two are concerned, there are many debates over what is better now, keyword being *now*. 64-bit will be the future, but at this point, virtually everything is catered to 32-bit. I don't want to turn this Thread into a debate, but just do a Forum Search for 64-bit and see how many debate Thread results show up. If higher memory is your only reason to go with 64-bit, it's not worth it. Unless some really cool Star Trek computer stuff happens with the industry, it will be a loooooong time before the average Home Users need anything even remotely close to 128 Gigs, hell even 8 Gigs.