Two Problems .. Apple store and XGPS Application...

Hi,
I am very new to Iphone. Infact I just got an Iphone 3G a few days back. It was already Jailbroken and Unlocked when I got it. So I hadnt had to do anything. During the last 2 days, I ve learned things about using various applications. My iphone has Cydia and ICY both installed.
I ve already installed applications from Cydia .. and they are working fine.
Question No 1... Can I also install using ICY ????
Question No 2... If i buy Apple store applications and install on my phone, will it cause any harm to iphone??? I am interested in the Motion GPS Application from apple store.
Question No 3. I downloaded the XGPS application from Cydia. Also to use offline maps, i downloaded XGPS Manager on my PC. However, the street maps for my region (Pakistan) are not available in XGPS Manager... Though google maps has the detailed street maps. Can someone suggest how i can use google maps on the xgps software.

WIll be thankful if someone can provide the answers.

Thanks and Regards
Fahad

1. Yes. You can install/modify/delete jailbroken applications using either Cydia or Icy.

2. No. Installing applications from the App Store will not harm your iPhone. That would defeat the purpose of Apple promoting the App Store so vigorously.

3. Not sure on that. XGPS works fine for me here in the USA. Someone else may have the answer.

thank you so much for your reply ...
now i ll try using the apple applications ..
will let you know if i have anymore questions ...