I've got both NTSC and PAL versions of back to nature, I noticed a lot of freezing up with the ntsc version. *But here's a tip or two.
1. *the freezing will only last a short amount of time, well actually sometimes it can happen for around 5 - 10 mins, you'll usually come across it when entering or exiting areas. *You can try being patient, just leaving the game where it is and hope it comes back on. *(I've found it usually does come back...eventually!).
2. *Put the playstation on a flat table, if possible construct some sort of free stand (prop it up by all four corners).
3. *Put the playstation on its side, and position a large fan so it blows at the underside (for cooling purposes).
4. *Have a cuppa, and a cigarette if you smoke.
5. *Buy a PS2, (it comes complete with it's own fan!:holidays2

*and I've found it seems a lot better on the ps2 anyway with regards to speed and such.
6. *Keep that controller handy 'cos it'll come back when you least expect it! and we all know times a commodity we can't afford to waste on this game.
*So far (touch wood) I haven't had a problem with the PAL version of the game, but then I've had to restart due to the change in formats, so I'm only in the first year with the PAL.
Happy Farming (I hope):erm:
edit:
Lucifer was right about too many things on screen. *I found my problems got far worse after getting married, and having 10 cows, sheep, chickens, 7 sprites coming to work, and lots of harvesting to be done!