Use a text editor such as notepad to edit the "DefaultGame.ini" file in the "C:\Games\Mass Effect\BioGame\Config" directory in Windows XP. Change any of the following lines to activate the corresponding cheat function.

To get more inventory space, set the value of the "m_nMaxInventoryItems" entry to "9999".
To increase your grenade capacity, change the value of the "m_nMaxGrenades" entry to any number up to "999".
To increase your Medigel capacity, change the value of the "m_fMaxMedigel" entry to any number up to "999".