Hello and welcome to GuildWars Guru. This is a community maintained website and forum and we are very helpfull. What we however do ask from out members is to search before asking. Only yesterday this is already asked in this very same forum (one spot below where your post is).
So my advice is to check out what myself and others had to say on this subject. If you have any more questions afterwards I kindly request you to reply in that threath.
There are 2 completely different games. If your only reason for buying GW 1 would be to get ready for GW 2 than you definitely shouldn't get it. The games are so much different that it will do the opposite. You'll get used to brilliant mechanics and gameplay of GW 1 and you'll just be disappointed when you see how much different GW 2 is.