You can do it as you described. Connect SRAM data and address buses as usual, /CS to address decoder (or GND, if this is the only external parallel device), /OE to /PSEN and /WE to /WR (/PSEN and /WR are signals of '51). Thus, for writing MOVX can be used, while reading can be accomplished using MOVC (and code can be run from it, of course). Be careful with the timing, which is more restrictive for external code memory than data memory (check the PSEN-related timing diagrams in datasheets).
The reset should involve also switching of a flip/flop driving the EA pin. And don't forget, that at certain protection level (security fuse programmed), external code execution is disabled!
Also, for similar approach check out
http://www.bezstarosti.cz/jungle/sc...ofreny.htm
although not in english, I think you will understand it.

However, there are also other options worth considering:
- you don't need "resetting"and remapping your code; you can have your external code memory (SRAM) mapped above the internal code memory and run it from there; after loading the code you simply jump to the external code.
- there are nonvolatile parallel memories,using which you don't need the serial eeprom and the "booting" from it - and also you don't need the "boot code" and internal code memory and reset/switchover mechanism at all, storing the "upgrader" in the same memory. External parallel FLASH memory is one such option, as Andy already pointed out; however, programming algorithms for different manufacturers' FLASH are not the same so for mass production you will need to stick to a particular brand. But you can also use a battery-backuped SRAM, either discrete battery+SRAM(+diode), or packed in one package - e.g.Dallas is producing such stuff, incorporating also a RTC. There are also SRAM-like, but nonvolatile memories, either using a ferroelectric memory cell (Ramtron - beware, needs clocked /CS) or having a background FLASH, where the contents of RAM is automatically written on power-down (see ZMD).

- the best you can use is a mcu capable of rewriting its own internal program FLASH - e.g. the RD2 - variety of '51 - the easiest to use is Atmel AT 89C51RD2 (or ED2 foe extra EEPROM), or alternatively also Philips P89V51RD2 can be used.

Jan Waclawek