Hi, I'm a game programmer that's been working on a project with my friend to create a multiplayer online version of his board game. We're using Smartfox Server for the game server, and also have a forum (phpBB) which is linked with the game. We're both still students and don't have that much money to spend, especially as ad revenue is slow and it's hard for us to spare the 30-40 dollars a month for hosting. Normally, I'd go with regular web hosting, but due to the game server, that's not an option.
The question is, how much RAM do I need? Disk space is trivial, since I don't forsee getting more that a few gigs of space filled up in the first place. However, I'm really worried about RAM. How much do I need?
Thanks!

Upgrades and downgrades are relatively painless (a few minutes of downtime and that's it), so I'd start with the 360 and see how it goes. If it turns out you need more RAM, open a ticket to move up to a 540 (or 720, or...) and it'll be done.

Yes, I know that Linode is really easy to upgrade or downgrade, but again, I have little money and basically can only afford the 360. If it turns out the 360 is not enough, I don't want to have spent 20 dollars on nothing. In that case, if the 360 is not enough, I'll stick with my current plan: using my own personal computer as the game server. (which is really, really not what I want)

well, how much RAM does your game server need ?
running a php powered site shouldn't take more than 100MB (depending on your exact setup, all depending on choice of web server, cache, DB, etc etc) so that leaves you with about 200 MB for your game server.
you probably have a test setup at home, no ?
so go and check how much resources it needs and then see if that fits into a Linode 360 if you subtract the memory needs for the web server.

Well, it's not the game server I'm worrying about, but the forum. I've read one too many stories about 256 MB RAM VPS's failing with a basic forum, and 384 is only 50% more. We don't get too many hits now, but that's mainly because the game is still in development and on a free host.

This is a Linode 360 running Ubuntu 8.04, Apache 2 using the prefork MPM, and a PunBB forum:

$  free -m
             total       used       free     shared    buffers     cached
Mem:           360        338         21          0          6        246
-/+ buffers/cache:         85        274
Swap:          255          0        255

MySQL is probably the biggest chunk out of that 85MB. The system also runs sshd and Postfix, but these contribute minimally to memory usage. I don't think I've ever seen swap get touched.

Of course, your results may vary based on differences between phpBB and PunBB and on traffic load (this server sees ~10,000 pageviews/day and ~45,000 raw hits/day).

OK, cool. I probably won't be getting that many views for a while, and when I do, ads will probably take care of most of the cost. Thanks!

Apache, PHP, sshd, Postfix, Dovecot:

jed@lachryma:~$ free -m
             total       used       free     shared    buffers     cached
Mem:           349        171        177          0         28         98
-/+ buffers/cache:         44        304
Swap:          511          0        511

360 stretches.