I am absolutely new to Linux and Ubuntu, so I would like to spend some time to try Ubuntu before a full installation. I have read a few pages about liveCD with persistent image and I have found it quite useful for my purpose (which is trying Ubuntu and, especially, its applications without messing with my laptop's Windows 7). Using the method explained in here, I have created an Ubuntu USB flash drive; however, I have seen that the OS is extremely slow in doing ordinary things (even web surfing, which leads to temporary gray screens in Firefox).
My question is if I install Ubuntu in such a way that the persistent image stays in one of the local partitions of the hard drive (instead of the USB flash drive), would it resolve the problem, or running OS from USB drive will result in a very slow OS anyway? Also, I am not sure how I can install Ubuntu on a flash drive and have one of local partitions on the hard drive be the persistent image. So, any help regarding that will be also appreciated.