If you are feeling unsure or worried then I would recommend not doing anything at all. Try looking around these forums and other sites and read what tohers have done and learn a bit more before tweeking your own system. If you want some hands on experience follow some of NickN's stickies dot for dot and it should keep you out of trouble. He is our computer guru and is much loved on these forums for his knowledge.
The problem your describing sounds as though the textures aren't loading fast enough, causing the lag and blurries. Have you tried defragging your hard drive? THis may help a little but the main problem would be your system isn't fast enough to handle all of the textures.
http://www.simviation.com/cgi-bin/yabb2 ... 1197380641 this thread should get you started nicely. It has instructions on how to set up FSX properly and also how to defrag. There is a section for XP in there, and I would recommend you skip it if you are using vista except for the part about defragging as it applies to both. If you don't understand anything in the thread post a thread in the FSX section and we'll be able to help you out