yum simulate install

you can do a yum install without the -y switch (if you use it):

yum install <package>

this will grab a list of packages and dependancies required. Before installing it will ask you if you want to install or not, just answer no and no changes will be made.

Alternatively you can do

yum deplist <package>

to list all the dependancies of a package and see what needs to be installed without downloading or installing anything.

You can use the check-update option to yum to see if there is an update available for the package. It will tell you if there is an update available (and to what version) for the specified package.

So you could do something like:

yum check-update <package> 

to see the info for a specific package, and:

yum check-update

to see the info for the whole system.