I currently have an old version of limewire and i was thinking about getting the new 4.10 PRO, if I install this over the top of my old version will that be ok? will it import my incomplete downloads so I can finish them?

Your incomplete's won't be affected but ...... what version of LW do you have? If your version is earlier than about 4.4 then you may need to use the add/remove control panel to remove LW before you reinstall. Otherwise the installer will remove the previous version of LW at the beginning of the installation process. Sometimes it's advised to delete the LW prefs folder before you update to pro. If you have any odd behaviour then do such. Try deleting your LW Preferences folder whilst LW is closed; instructions here: Point #2 & 3 in Fixes for Limewire (sample image included at bottom of page.)

i have 4.9

That should be fine! But still ... if you have any probs after updating to pro, delete your LW prefs folder whilst LW is closed!

will upgrading to 4.10 find more stuff?

I found 4.10.9 & 4.11.0 beta better than the previous verions for searching. But everyone's experience to their own situation. You may not find the same improvements. Sometimes versions can be set-up specific as to how well they perform.

if i dont like 4.10 can i downgrade to 4.9 ? i dont think i like it, the program seems to lag with downloads going

As said, delete the LW prefs if it isn't behaving as well. Other than that, learn to use it bit by bit. It does have its advantages over earlier versions. But as I earlier suggested, this might also be set up specific. I found it better both on my mac & pc windows. But it does have some slightly different characteristics that need time to adapt to. Give it some time before making rash decisions about its abilities. Also, new downlds will behave better than older ones that were started with LW 4.9!!! So keep that in mind. I found that to be very true. I was also initially a little disappointed until I initiated & completed the downld process totally thru 4.10 or 4.11 beta which I've now been using for a while now.

(LW.org do not offer older versions. If you're really desperate for an earlier version then apply thru me via pm & I'll see what I can do. It will require some convincing though, including as many of your set up details, etc. as possible! There's very good reasons why LW doesn't offer older versions!)