Unfortanatly, no.
No you cannot go to other regions in Pokemon Pearl or Diamond version but in Pokemon Heart Gold and Soul Silver you can go to the Jotoh region.
quick claw
The entirety of Pokemon Pearl and Diamond is set in the Sinnoh region. There is no way to revisit any of the other Pokemon world regions.
Go to stark mountain and other places you couldn't go efore you beat the Pokemon leaque
No you cant catch one alone with no other game but if you have ruby insert it into the ds with Pokemon pearl and go on Pokemon pearl and go to Route 203 or Route 204 after obtaining the national pokedex. (Rudy game inserted)
When you receive it, go play Pokemon Pearl and go to the pokemart.
You can get the Pokemon in Sinnoh. If you go to Pokemon.com, you can see them.
You can go on gamespot.co.UK and search for Pokemon pearl
Its already preloaded in the action replay so go get it.
Pokemon #46 is Wormadam. If you need any other help go to www.pokemon.marriland.com On the side in the diamond and pearl section it has a pokedex option, click there and you will see all the pokemon.
because they want get out of there country
In Pokemon Pearl version, go to a Pokemon center, up the stairs, you will see doors. go to the second door. the lady will let you in the trading room. (at least 2 other people near you playing must be in that room)