You can try 6502, Z80, 68000 and ARM Assembler from the discomfort of your own Windows PC.
6502: http://www.6502.org/tools/emu/
68000: http://www.easy68k.com/
Z80: http://www.z80.info/z80sdt.htm#SDT_ASM_W32
ARM: http://arm.flatassembler.net/ http://arm.flatassembler.net/ or get a Rasberry Pi, you really should.
This may be considered cheating, but I realize that not everybdy has the room for lots of old computers!