i've just installed wubi, i thought it will rub on windows itself but the fact that when i turn my computer on i choose between windows and ubuntu from the menu ...anyways its my first time to use linux.
During installation i was aked to choose a username and password,i did...and when i open ubuntu it asks me to enter the username and password ,but i fogot them :< ...is there anything i can do to rememeber them ? and where can i find tutorials about wubi ?

First, some semantics.....If I understand correctly, WUBI is a tool to install Ubuntu Linux from Windows. Once installed, you will be looking for info on how to run Ubuntu.

If you are new to Linux and to Linux/Unix terminal commands, you might find it easier to simply re-install.

You cannot recover a forgotten password, but you CAN get into Ubuntu to make a new one.

Re-boot the computer and--when you get the boot menu, hit any key to stop the countdown. Then "escape" (if necessary--to get out of the graphical GRUB display) and then "e" to get into editing mode. Add the word "single" at the end of the kernel line, hit enter to save the change and then boot. (I'm fuzzy on the exact details, but there are some on-screen prompts that will help get the exact steps right.)
This takes you to a root terminal with no password required.

Once you are in Linux, then enter "more /etc/passwd" and look for the username that you used when installing.

finally, enter "passwd username" , enter a new password, and then "reboot". When the computer comes back up in Linux you will be able to log in with your username.

there is grub ...its just enter to brown backgrund of ubuntu and ask for username and password ...

i mean there is no grub*

Is this machine set up to dual-boot with Linux and Windows? If so, is there not a menu which allows you to choose? If so, that is the GRUB menu.

Even if it is Linux only, GRUB has to be there. Depending on your settings, it might appear for only a few seconds. When you boot up, watch for "grub loading" followed by a menu. As soon as you see it, hit a key to stop the countdown. (You might have to hit a key during bootup to show details---sometimes it will say "verbose")