laptop hard drive

[ONESHOTKILL]

i have a laptop which is a HP omnibook XE4100 and it has a 30gb hdd i would like to put a bigger hdd in it.How easy is it to replace the harddrives in laptops? and also do some laptops only support curtain size hdds.I was also thinking about getting a dvdrw drive for it but is that also possible to change dvd drives in laptops?

 

[ONESHOTKILL]

ok thanks for that,i downloaded the manual and it has the info on replacing the hdd ect which is helpful.Just wounder what size would fit in it,i was thinking about buying a 80gb and seeing if that works