Haaaaalp?!

Ok, I'm currently being hosted with Dreamhost.com, but my domain is with FXDomains.com. How do I make it so that the domain I have at FXDomains.com will work like the domain I have at Dreamhost.com, for example FXDomains.com provides me with the domain x.com, however Dreamhost.com provides me with y.com. I want to make it so that when someone goes to x.com, it behaves like y.com, such as x.com/forums would go the same place as y.com/forums It's not domain forwarding, it's something ro do with DNS or something. I changed my FXDomains.com's DNS thing to NS1.DREAMHOST.COM, NS2.DREAMHOST.COM & NS3.DREAMHOST.COM so what do I do now?

I think you can simply add a CNAME entry to the Dreamhost name servers aliasing x to y.  If you have access to the entries, that is, I do with my server, it's a blessing.