New Graphics / Video Card for a DELL Inspiron 9400

My newest Laptop is a DELL Inspiron 9400.  It has a NiVidia 256MB GeForce 7900 graphics / video card.   I work with fairly complex Architectural Designs, and would like to upgrade my graphics / video card to keep pace with the latest release of the Architectural and Structural Engineering software.  I would like to install an NVIDIA GeForce 7950 GX2 1GB  card; however, there are three different models of this card, each configured slightly different than the others.  Which one of the three would be best suited for my system considering the demanding Archi-

tectural software that I must use.   Also, is it very difficult to exchange the cards ?  Once I have disconnected all power sources ( A/C & Battery ), discharged any kinetic electricity that I or my system may be radiating, soundly & fully grounding the Laptop, and carefulling stabalizing it atop my work table, is it merely a matter of disconnecting the older graphics / video card in my system, and then very slowly and carefully remove it; and, then follow the exact procedure " in reverse " being slow, carefully deliberate, and not forcing the NVIDIA GeForce 7950 GX2 1GB  into the slot freed up by my removal of the 256MB GeForce 7900 card.  And, when I speak of "not forcing" the card into the vacant slot, I mean that I am being extremely careful not to push / place the new card into its correct position and location until everything is perfectly aligned allowing the new 1.0GB graphics card to very gently slide / snap " into place "  without meeting any kind of small resistance what-so-ever.   If I follow this procedure, will I be able to exchange the cards fairly easily; or, should I take it to an authorized DELL warranty & repair shop where I may be charged well over $100.00 for inserting a new card that has an average retail of about $585.00.  Also, as I noted earlier, which one of the three 1.0GB GeForce 7950 graphics / video card would be the best for my system, or is just maybe the best one overall ??  I noticed that among the three 1.0GB cards, there appears to be an average price difference of $20 to $30 from one card to what I would guess is the next card up.    I sincerely hope that there is someone out there that can be of great assistance to me, and will be able to tell me the difference(s) between the three cards, the best " card-of-record " for my system and the software I use.........or, whether I should just buy the best card of the three since there's only about $60.00 to $75.00 between the lowest and the highest card.  And, also if I will be "okay" removing the older card, and inserting the new 1.0GB card myself ?   I would be so very grateful for any advice, information, direction(s), and patience that anyone out there may be able to offer.   And, in advance, I will be so very truly grateful and appreciative.  Good evening to all, and wishing everyone a very safe and pleasant weekend approaching ahead !!