Hello.
I decided that I'd give learning 6502 assembly another try, since I just learned how to use DOS to a decent extent[thanks creaothceann]. I've got a couple disassemblers working, Tracer and something simply called 6502 Disassembler. I disassembled a SMB3 rom on each. Then my problem arose: I couldn't get an assembler to work. WLA-DX said "not enough memory." o.0 From what I understand, 6502 and 65816 are almost identical. So I tried byuu's xkas, and it appears that BOTH disassemblers gave an odd dump, because I got several hundred "invalid opcode" errors before I closed it.
This is a sample of the dump from Tracer:

And a snippet from "6502 Disasembler"

I'm really confused. I guess when it disassembles, it's not in the right form to assemble again. I also noticed that these files use X and Y. Am I confused again, or am I correct that 6502 only has the accumulator? I had hoped that once I had learned how to use the damn MS-DOS shell that I would have no problems assembling and disassembling, but this pops up. Am I using the wrong disassembler, assembler, both, or am I just retarded?
I would greatly appreciate any help. Thanks.

I'm not really experienced with assembly on these processors, but it looks like the tracer outputted the address of the code and it's value in hex as well as the code. To compile it you should just have things like this (using your examples):

You could try emulators like DOSBox or MS Virtual PC.

Note that working in DOS is much easier with a file manager like Norton Commander.

Another thing is that the NES can only handle 16-bit addressing, so instructions with 3-byte addresses won't work.
Also, doing a full ROM disassembly isn't a very good idea, since it will also try to decode data within the code, very possibly screwing up whatever real code followed.
I could go on more about how Tracer's code isn't easily reassemblable, but I don't have time.