Help what should i buy

ok, i am thinking of buying guild wars platinium which is prophecies and eye of the north expansion..... my question is can I play all classes?

No. You will not be able to play Dervish, Paragon, Assassin, or Ritualist. You need Nightfall to create a Dervish or Paragon and you need Factions to create an Assassin or Ritualist.

dam....... i cant find where to buy trilogy.. (not on the net)

I actually just saw it at Target on Wednesday. If you have one of those in your area, try there. I would think Best Buy would have it also.

Saw it as well at Target I also think newegg has the trilogy pack

^ he said not over the net

target i also saw one there.

over the net
amazon.com
plus about 100 other online stores
if u can't find it ur not trying very hard

If you're going to consider purchasing Guild Wars, your best bet would be to purchase over the internet (at a site such as Newegg, simply due to the fact that Guild Wars is an older game, and not all stores will carry it on their shelves.

If you insist on buying them from the store itself, you may have to specially order the game by calling in and seeing if they'll even order it for you.

As for "which to buy", that's up to you. You can purchase the entire game for a little under $50 (USD), which isn't a lot now. (Compared to the $30-$50/ea when they all came out - not including BMP/Collector Editons.) When I say "entire game", I mean Prophecies, Factions, Nightfall, and Eye of the North.

If you're only able to afford one, you'll have to decide on what type of gameplay you like.
-Prophecies has a great storyline, and can be difficult at times. Sadly, there is not a lot of PvP, and (even with the update to them,) the henchmen are not that great. Heroes are NOT INCLUDED.
-Factions has a fairly good storyline as well, but the Factions game release was the biggest PvP "update" that the game has ever seen. Alliance Battles, Fort Aspenwood, Jade Quarry, and having to choose sides (Luxon/Kurzick).
-Nightfall has a good, structured storyline, and was the first to add/include Heroes into the game. Heroes, if you didn't know, are basically customizable henchmen - you can give them items, upgrade their armor, change their skills, etc.
-Eye of the North is a good storyline, fairly short though - you must realize, that it is not a stand-alone campaign like the other three. It requires you to own one of the campaigns in order to explore it.

Your choices are really based on if you're more for PvE or more for PvP. All three campaigns do allow you to PvE and PvP, but some more than others. (If you don't own Factions, you are not able to participate in Alliance Battles, or any of the other Factions-related PvP areas/zones.)

I second the vote for newegg. Good prices on various Guild Wars incarnations. Prophecies/EotN Platinum is best deal at $9.99 shipped.
When in stock, Trilogy is 36.99 shipped.