If you have a PowerPC, you can run Leopard, although I can understand why you want to keep Tiger.
Contrary to what somebody said, in order to upgrade from Tiger to Snow Leopard (if you have Intel Mac), you legally need a full SL install package. The £29 - or whatever it costs in your country - applies to upgrading from Leopard.
My suggestion is to either to upgrade to Leopard or to buy a cheap PC or Intel Mac (is there such a thing?). Also, you might get a cheap eMac or something on which you might run Leopard, if you fancy another PPC. I actually have two old eMacs and I was surprised how snappy they are with some RAM and HDD upgrade. In fact, I have the same amount of RAM in one of them as I have in my MacBook Air.