Rajani, A HEARTY WELCOME TO TM...
Now about ur questions, if u r on H4, u can't apply for an asstship and u can't even take up any jobs..U r literally a "DEPENDANT" on ur spouse for ur tuition and also living expenses....Remember that tuition costs for an MS can go as high as $5000 per semester depending on the number of courses u take per semester (or quarter in some univs)...On the other hand, if u get an F1 VISA u can get an asstship or in the worst case, if u dont get an asstship, u can atleast work in some oncampus jobs and earn some $$$$.... But, u can't change ur VISA from a H4 to F1 unless u get an I-20 from atleast one US Univ....After u get ur I-20 u can go to Canada (or India) and get ur F1 VISA.....So to get an I-20 u gotta take ur GRE, TOEFL and apply for the universities......Its the same process as a student in India should go thru, that a H4 VISA holder have to follow even though they r here in the US.
If u have any more questions about VISAs and stuff visit
http://www.immigrationportal.com...and if u have any questions about any of the tests, u already did a great job by joining our community
HTH
-Sri.