Ah cool, I kinda got quite a bit of money and decided to blow a quarter of it on games.
You should try and get skate 2 (DE) as at the moment, I can't be bothered with the online as i've already done it once haha.
Well the online ones consist of the challanges and the online multiplayer.
149 co-op challanges have to be complete with your custom skater to get some of the achievements
5,000 EXP and some medal stuff has to be complete to get the multiplayer achievements. I have everything written down at my apartment which I'm about to leave to. I've been at my parent's house/out of town this weekend since us Americans had a holiday this weekend. Give me a few hours and I'll get back to you or if you're going to pass out soon I'll just tell you tomorrow.
Something was mentioned in the achievement guide about not installing the DLCs until after you get the multiplayer achievements because appearently people have problems with them unlocking with the DLCs installed.
This exerpt is from x360a acheivement guide:
If you have any Downloadable Content while working towards the online challenges you may need to remove them once you get to the end of your challenges. Users have reported that the DLC blocks the achievement, there isn't a patch but removing the DLC and replaying a challenge will unlock the achievement. I suggest you avoid DLC if you want to complete the full retail 1000 without any hiccups.